Semiconductor device wherein a property of a first semiconductor layer is different from a property of a second semiconductor layer

ABSTRACT

It is an object to provide a semiconductor device which has a large size and operates at high speed. A top gate transistor which includes a semiconductor layer of single-crystal and a bottom gate transistor which includes a semiconductor layer of amorphous silicon (microcrystalline silicon) are formed over the same substrate. Then, gate electrodes of each transistor are formed with the same layer, and source and drain electrodes are also formed with the same layer. Thus, manufacturing steps are reduced. In other words, two types of transistors can be manufactured by adding only a few steps to the manufacturing process of a bottom gate transistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object, a method, or a method forproducing an object. The present invention relates to a display deviceor a semiconductor device, in particular. The present invention relatesto a display device or a semiconductor device which is formed bysingle-crystal being transferred to a glass substrate, in particular.

2. Description of the Related Art

In recent years, flat panel displays such as liquid crystal displaydevices and electroluminescence (EL) display devices have attractedattention.

Driving methods of the flat panel displays include a passive matrixmethod and an active matrix method. An active matrix method hasadvantages over a passive matrix method such as the facts that powerconsumption is lowered, definition is heightened, a larger substrate canbe used, and the like.

In a structure where a driver circuit is provided outside the panel, itis possible to use an IC using single-crystal silicon as a drivercircuit; therefore, a problem due to a speed of a driver circuit doesnot arise. However, when an IC is provided in this manner, themanufacturing cost cannot be reduced sufficiently because of necessityof preparing a panel and an IC separately, necessity of a step ofconnecting the panel and the IC, and the like.

Thus, in view of reducing the cost or the like, a method in which apixel portion and a driver circuit are formed over the same substratehas been employed (for example, see Reference 1: Japanese PublishedPatent Application No. H8-6053).

SUMMARY OF THE INVENTION

In the case shown in Reference 1, non-single-crystal silicon such asamorphous silicon, microcrystalline silicon, or polycrystalline siliconis used as a semiconductor layer of a driver circuit, similarly to thepixel portion. However, even in a case where microcrystalline silicon orpolycrystalline silicon as well as amorphous silicon is used, there is aproblem in that characteristics thereof are incomparable tocharacteristics of single-crystal silicon. In particular, in asemiconductor layer which is used for a conventional panel where adriver circuit is integrated, mobility which is necessary and sufficientis not obtained. This has caused a big problem in manufacturing asemiconductor device of which high speed operation is required, that is,a driver circuit.

With the foregoing problems in consideration, an object of the presentinvention is to provide a semiconductor device manufactured with lowcost. Alternatively, another object of the present invention is toprovide a semiconductor device provided with a circuit which can operateat high speed. Alternatively, another object of the present invention isto provide a semiconductor device which consumes low power.

In the present invention, a silicon layer is separated from asingle-crystal substrate, and bonded (transferred) to a glass substrate.Alternatively, a single-crystal substrate is bounded to a glasssubstrate, and the single-crystal substrate is separated to form asilicon layer over the glass substrate. Then, the silicon layer isprocessed into an island shape. After that, a silicon layer is separatedfrom the single-crystal substrate again and bonded to the glasssubstrate. Alternatively, the single-crystal substrate is bonded to theglass substrate, and the single-crystal substrate is separated to formthe silicon layer over the glass substrate. Then, the silicon layer isprocessed into an island-shape again.

Then, TFTs are formed over the glass substrate using these siliconlayers.

At this time, a TFT using amorphous silicon or microcrystalline siliconis also formed at the same time.

Then, in these TFTs, a conductive layer serving as a gate electrode or aconductive layer serving as a source electrode or a drain electrode areshared, and these conductive layers are formed at the same time. Thus,the number of manufacturing steps can be reduced.

The present invention includes a first semiconductor layer over aninsulating substrate, a first insulating layer over the firstsemiconductor layer, a first conductive layer and a second conductivelayer over the first insulating layer, a second insulating layer overthe first conductive layer and the second conductive layer, a secondsemiconductor layer over the second insulating layer, a third conductivelayer over the second semiconductor layer, a fourth conductive layerover the second insulating layer, a third insulating layer over thethird conductive layer and the fourth conductive layer, and a fifthconductive layer over the third insulating layer. The firstsemiconductor layer serves as an active layer of a first transistor. Thesecond semiconductor layer serves as an active layer of a secondtransistor. A property of the first semiconductor layer is differentfrom a property of the second semiconductor layer.

A feature of the present invention, in the structure, is that the firstinsulating layer serves as a gate insulating layer of the firsttransistor, and the first conductive layer serves as a gate electrode ofthe first transistor.

A feature of the present invention, in the structure, is that the secondinsulating layer serves as a gate insulating layer of the secondtransistor, and the second conductive layer serves as a gate electrodeof the second transistor.

A feature of the present invention, in the structure, is that the fifthconductive layer is electrically connected to the fourth conductivelayer through a contact hole provided in the third insulating layer.

A feature of the present invention, in the structure, is that the fifthconductive layer is electrically connected to the first semiconductorlayer through a contact hole provided in the first insulating layer, theinsulating layer and the third insulating layer.

A feature of the present invention, in the structure, is that the thirdconductive layer is electrically connected to the second semiconductorlayer.

A feature of the present invention, in the structure, is that the firstsemiconductor layer has crystallinity.

A feature of the present invention, in the structure, is that the secondsemiconductor layer includes an amorphous semiconductor.

A feature of the present invention, in the structure, is that the secondsemiconductor layer includes a microcrystalline semiconductor.

Note that various types of switches can be used as a switch. Anelectrical switch, a mechanical switch, and the like are given asexamples. That is, any element can be used as long as it can control acurrent flow, without limiting to a certain element. For example, atransistor (e.g., a bipolar transistor or a MOS transistor), a diode(e.g., a PN diode, a PIN diode, a Schottky diode, an MIM (metalinsulator metal) diode, an MIS (metal insulator semiconductor) diode, ora diode-connected transistor), a thyristor, or the like can be used as aswitch. Alternatively, a logic circuit combining such elements can beused as a switch.

An example of a mechanical switch is a switch formed using MEMS (microelectro mechanical system) technology, such as a digital micromirrordevice (DMD). Such a switch includes an electrode which can be movedmechanically, and operates by controlling connection and non-connectionbased on movement of the electrode.

In the case of using a transistor as a switch, polarity (a conductivitytype) of the transistor is not particularly limited because it operatesjust as a switch. However, a transistor of polarity with smalleroff-current is preferably used when off-current is to be suppressed.Examples of a transistor with smaller off-current are a transistorprovided with an LDD region, a transistor with a multi-gate structure,and the like. In addition, it is preferable that an N-channel transistorbe used when a potential of a source terminal is closer to a potentialof a low-potential-side power supply (e.g., Vss, GND, or 0 V), while aP-channel transistor be used when the potential of the source terminalis closer to a potential of a high-potential-side power supply (e.g.,Vdd). This is because the absolute value of gate-source voltage can beincreased when the potential of the source terminal is closer to apotential of a low-potential-side power supply in an N-channeltransistor and when the potential of the source terminal is closer to apotential of a high-potential-side power supply in a P-channeltransistor, so that the transistor can be operated more accurately as aswitch. This is also because the transistor does not often perform asource follower operation, so that reduction in output voltage does notoften occur.

Note that a CMOS switch may be used as a switch by using both N-channeland P-channel transistors. When a CMOS switch is used, the switch canmore precisely operate as a switch because current can flow when eitherthe P-channel transistor or the N-channel transistor is turned on. Forexample, voltage can be appropriately output regardless of whethervoltage of an input signal to the switch is high or low. In addition,since a voltage amplitude value of a signal for turning on or off theswitch can be made smaller, power consumption can be reduced.

Note that when a transistor is used as a switch, the switch includes aninput terminal (one of a source terminal and a drain terminal), anoutput terminal (the other of the source terminal and the drainterminal), and a terminal for controlling conduction (a gate terminal).On the other hand, when a diode is used as a switch, the switch does nothave a terminal for controlling conduction in some cases. Therefore,when a diode is used as a switch, the number of wirings for controllingterminals can be further reduced compared to the case of using atransistor as a switch.

Note that when it is explicitly described that “A and B are connected”,the case where A and B are electrically connected, the case where A andB are functionally connected, and the case where A and B are directlyconnected are included therein. Here, each of A and B corresponds to anobject (e.g., a device, an element, a circuit, a wiring, an electrode, aterminal, a conductive film, or a layer). Accordingly, another elementmay be interposed between elements having a connection relation shown indrawings and texts, without limiting to a predetermined connectionrelation, for example, the connection relation shown in the drawings andthe texts.

For example, in the case where A and B are electrically connected, oneor more elements which enable electric connection between A and B (e.g.,a switch, a transistor, a capacitor, an inductor, a resistor, and/or adiode) may be provided between A and B. In addition, in the case where Aand B are functionally connected, one or more circuits which enablefunctional connection between A and B (e.g., a logic circuit such as aninverter, a NAND circuit, or a NOR circuit, a signal converter circuitsuch as a DA converter circuit, an AD converter circuit, or a gammacorrection circuit, a potential level converter circuit such as a powersupply circuit (e.g., a dc-dc converter, a step-up dc-dc converter, or astep-down dc-dc converter) or a level shifter circuit for changing apotential level of a signal, a voltage source, a current source, aswitching circuit, or an amplifier circuit such as a circuit which canincrease signal amplitude, the amount of current, or the like (e.g., anoperational amplifier, a differential amplifier circuit, a sourcefollower circuit, or a buffer circuit), a signal generating circuit, amemory circuit, and/or a control circuit) may be provided between A andB. Alternatively, in the case where A and B are directly connected, Aand B may be directly connected without interposing another element oranother circuit therebetween.

Note that when it is explicitly described that “A and B are directlyconnected”, the case where A and B are directly connected (i.e., thecase where A and B are connected without interposing another element oranother circuit therebetween) and the case where A and B areelectrically connected (i.e., the case where A and B are connected byinterposing another element or another circuit therebetween) areincluded therein.

Note that when it is explicitly described that “A and B are electricallyconnected”, the case where A and B are electrically connected (i.e., thecase where A and B are connected by interposing another element oranother circuit therebetween), the case where A and B are functionallyconnected (i.e., the case where A and B are functionally connected byinterposing another circuit therebetween), and the case where A and Bare directly connected (i.e., the case where A and B are connectedwithout interposing another element or another circuit therebetween) areincluded therein. That is, when it is explicitly described that “A and Bare electrically connected”, the description is the same as the casewhere it is explicitly only described that “A and B are connected”.

Note that a display element, a display device which is a device having adisplay element, a light-emitting element, and a light-emitting devicewhich is a device having a light-emitting element of the presentinvention can use various types and can include various elements. Forexample, a display medium, whose contrast, luminance, reflectivity,transmittivity, or the like changes by an electromagnetic action, suchas an EL (electro-luminescence) element (e.g., an EL element includingorganic and inorganic materials, an organic EL element, or an inorganicEL element), an electron emitter, a liquid crystal element, electronicink, an electrophoresis element, a grating light valve (GLV), a plasmadisplay panel (PDP), a digital micromirror device (DMD), a piezoelectricceramic display, or a carbon nanotube can be used as a display element,a display device, a light-emitting element, or a light-emitting device.Note that display devices using an EL element include an EL display;display devices using an electron emitter include a field emissiondisplay (FED), an SED-type flat panel display (SED: surface-conductionelectron-emitter display), and the like; display devices using a liquidcrystal element include a liquid crystal display (e.g., a transmissiveliquid crystal display, a transflective liquid crystal display, areflective liquid crystal display, a direct-view liquid crystal display,or a projection liquid crystal display); and display devices usingelectronic ink or an electrophoresis element include electronic paper.

Note that an EL element is an element having an anode, a cathode, and anEL layer interposed between the anode and the cathode. Note that as anEL layer, a layer utilizing light emission (fluorescence) from a singletexciton, a layer utilizing light emission (phosphorescence) from atriplet exciton, a layer utilizing light emission (fluorescence) from asinglet exciton and light emission (phosphorescence) from a tripletexciton, a layer formed of an organic material, a layer formed of aninorganic material, a layer formed of an organic material and aninorganic material, a layer including a high-molecular material, a layerincluding a low molecular material, a layer including a low-molecularmaterial and a high-molecular material, or the like can be used. Notethat the present invention is not limited to this, and various ELelements can be used as an EL element.

Note that an electron emitter is an element in which electrons areextracted by high electric field concentration on a pointed cathode. Forexample, as an electron emitter, a Spindt type, a carbon nanotube (CNT)type, a metal-insulator-metal (MIM) type in which a metal, an insulator,and a metal are stacked, a metal-insulator-semiconductor (MIS) type inwhich a metal, an insulator, and a semiconductor are stacked, a MOStype, a silicon type, a thin film diode type, a diamond type, a surfaceconduction emitter SCD type, a thin film type in which a metal, aninsulator, a semiconductor, and a metal are stacked, a HEED type, an ELtype, a porous silicon type, a surface-conduction (SED) type, or thelike can be used. However, the present invention is not limited to this,and various elements can be used as an electron emitter.

Note that a liquid crystal element is an element which controlstransmission or non-transmission of light by optical modulation actionof a liquid crystal and includes a pair of electrodes and a liquidcrystal. Note that optical modulation action of a liquid crystal iscontrolled by an electric filed applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). Note that the following can be used for a liquidcrystal element: a nematic liquid crystal, a cholesteric liquid crystal,a smectic liquid crystal, a discotic liquid crystal, a thermotropicliquid crystal, a lyotropic liquid crystal, a low-molecular liquidcrystal, a high-molecular liquid crystal, a ferroelectric liquidcrystal, an anti-ferroelectric liquid crystal, a main-chain liquidcrystal, a side-chain high-molecular liquid crystal, a plasma addressedliquid crystal (PALC), a banana-shaped liquid crystal, and the like. Inaddition, the following can be used as a diving method of a liquidcrystal: a TN (twisted nematic) mode, an STN (super twisted nematic)mode, an IPS (in-plane-switching) mode, an FFS (fringe field switching)mode, an MVA (multi-domain vertical alignment) mode, a PVA (patternedvertical alignment) mode, an ASV (advanced super view) mode, an ASM(axially symmetric aligned microcell) mode, an OCB (optical compensatedbirefringence) mode, an ECB (electrically controlled birefringence)mode, an FLC (ferroelectric liquid crystal) mode, an AFLC(anti-ferroelectric liquid crystal) mode, a PDLC (polymer dispersedliquid crystal) mode, a guest-host mode, and the like. Note that thepresent invention is not limited to this, and various liquid crystalelements and driving methods can be used as a liquid crystal element anda driving method thereof.

Note that electronic paper corresponds to a device which displays animage by molecules which utilize optical anisotropy, dye molecularorientation, or the like; a device which displays an image by particleswhich utilize electrophoresis, particle movement, particle rotation,phase change, or the like; a device which displays an image by movingone end of a film; a device which displays an image by using coloringproperties or phase change of molecules; a device which displays animage by using optical absorption by molecules; and a device whichdisplays an image by using self-light emission by bonding electrons andholes. For example, the following can be used for electronic paper:microcapsule electrophoresis, horizontal electrophoresis, verticalelectrophoresis, a spherical twisting ball, a magnetic twisting ball, acolumnar twisting ball, a charged toner, electro liquid powder, magneticelectrophoresis, a magnetic thermosensitive type, an electrowettingtype, a light-scattering (transparent-opaque change) type, a cholestericliquid crystal and a photoconductive layer, a cholesteric liquid crystaldevice, a bistable nematic liquid crystal, a ferroelectric liquidcrystal, a liquid crystal dispersed type with a dichroic dye, a movablefilm, coloring and decoloring properties of a leuco dye, a photochromicmaterial, an electrochromic material, an electrodeposition material,flexible organic EL, and the like. Note that the present invention isnot limited to this, and a variety of electronic paper can be used aselectronic paper. Here, when microcapsule electrophoresis is used,defects of electrophoresis, which are aggregation and precipitation ofphoresis particles, can be solved. Electro liquid powder has advantagessuch as high-speed response, high reflectivity, wide viewing angle, lowpower consumption, and memory properties.

Note that a plasma display has a structure in which a substrate having asurface provided with an electrode and a substrate having a surfaceprovided with an electrode and a minute groove in which a phosphor layeris formed face each other at a narrow interval and a rare gas is sealedtherein. Note that display can be performed by applying voltage betweenthe electrodes to generate an ultraviolet ray so that a phosphor emitslight. Note that the plasma display may be a DC-type PDP or an AC-typePDP. For the plasma display, AWS (address while sustain) driving, ADS(address display separated) driving in which a subframe is divided intoa reset period, an address period, and a sustain period, CLEAR(high-contrast low energy address and reduction of false contoursequence) driving, ALIS (alternate lighting of surfaces) method, TERES(technology of reciprocal sustainer) driving, or the like can be used.Note that the present invention is not limited to this, and variousplasma displays can be used as a plasma display panel.

Note that electroluminescence, a cold cathode fluorescent lamp, a hotcathode fluorescent lamp, an LED, a laser light source, a mercury lamp,or the like can be used as a light source of a display device in which alight source is necessary, such as a liquid crystal display (atransmissive liquid crystal display, a transflective liquid crystaldisplay, a reflective liquid crystal display, a direct-view liquidcrystal display, or a projection liquid crystal display), a displaydevice using a grating light valve (GLV), or a display device using adigital micromirror device (DMD). Note that the present invention is notlimited to this, and various light sources can be used as a lightsource.

Note that various types of transistors can be used as a transistor,without limiting to a certain type. For example, a thin film transistor(TFT) including a non-single-crystal semiconductor film typified byamorphous silicon, polycrystalline silicon, microcrystalline (alsoreferred to as semi-amorphous) silicon, or the like can be used. In thecase of using the TFT, there are various advantages. For example, sincethe TFT can be formed at temperature lower than that of the case ofusing single-crystal silicon, manufacturing cost can be reduced or amanufacturing apparatus can be made larger. Since the manufacturingapparatus is made larger, the TFT can be formed using a large substrate.Therefore, many display devices can be formed at the same time at lowcost. In addition, a substrate having low heat resistance can be usedbecause of low manufacturing temperature. Therefore, the transistor canbe formed using a light-transmitting substrate. Accordingly,transmission of light in a display element can be controlled by usingthe transistor formed using the light-transmitting substrate.Alternatively, part of a film which forms the transistor can transmitlight because the film thickness of the transistor is thin. Therefore,the aperture ratio can be improved.

Note that when a catalyst (e.g., nickel) is used in the case of formingpolycrystalline silicon, crystallinity can be further improved and atransistor having excellent electric characteristics can be formed.Accordingly, a gate driver circuit (e.g., a scan line driver circuit), asource driver circuit (e.g., a signal line driver circuit), and/or asignal processing circuit (e.g., a signal generation circuit, a gammacorrection circuit, or a DA converter circuit) can be formed over thesame substrate as a pixel portion.

Note that when a catalyst (e.g., nickel) is used in the case of formingmicrocrystalline silicon, crystallinity can be further improved and atransistor having excellent electric characteristics can be formed. Atthis time, crystallinity can be improved by just performing heattreatment without performing laser light irradiation. Accordingly, agate driver circuit (e.g., a scan line driver circuit) and part of asource driver circuit (e.g., an analog switch) can be formed over thesame substrate. In addition, in the case of not performing laser lightirradiation for crystallization, crystallinity unevenness of silicon canbe suppressed. Therefore, a clear image can be displayed.

Note that polycrystalline silicon and microcrystalline silicon can beformed without using a catalyst (e.g., nickel).

Note that it is preferable that crystallinity of silicon be improved topolycrystalline, microcrystalline, or the like in the whole panel;however, the present invention is not limited to this. Crystallinity ofsilicon may be improved only in part of the panel. Selective increase incrystallinity can be achieved by selective laser irradiation or thelike. For example, only a peripheral driver circuit region excludingpixels may be irradiated with laser light. Alternatively, only a regionof a gate driver circuit, a source driver circuit, or the like may beirradiated with laser light. Further alternatively, only part of asource driver circuit (e.g., an analog switch) may be irradiated withlaser light. Accordingly, crystallinity of silicon can be improved onlyin a region in which a circuit needs to be operated at high speed. Sincea pixel region is not particularly needed to be operated at high speed,even if crystallinity is not improved, the pixel circuit can be operatedwithout problems. Since a region, crystallinity of which is improved, issmall, manufacturing steps can be decreased, throughput can beincreased, and manufacturing cost can be reduced. Since the number ofnecessary manufacturing apparatus is small, manufacturing cost can bereduced.

A transistor can be formed by using a semiconductor substrate, an SOIsubstrate, or the like. Thus, a transistor with few variations incharacteristics, sizes, shapes, or the like, with high current supplycapacity, and with a small size can be formed. When such a transistor isused, power consumption of a circuit can be reduced or a circuit can behighly integrated.

A transistor including a compound semiconductor or an oxidesemiconductor such as ZnO, a-InGaZnO, SiGe, GaAs, IZO, ITO, or SnO, athin film transistor obtained by thinning such a compound semiconductoror an oxide semiconductor, or the like can be used. Thus, manufacturingtemperature can be lowered and for example, such a transistor can beformed at room temperature. Accordingly, the transistor can be formeddirectly on a substrate having low heat resistance, such as a plasticsubstrate or a film substrate. Note that such a compound semiconductoror an oxide semiconductor can be used for not only a channel portion ofthe transistor but also other applications. For example, such a compoundsemiconductor or an oxide semiconductor can be used as a resistor, apixel electrode, or a light-transmitting electrode. Further, since suchan element can be formed at the same time as the transistor, cost can bereduced.

A transistor formed by using an inkjet method or a printing method, orthe like can be used. Accordingly, a transistor can be formed at roomtemperature, can be formed at a low vacuum, or can be formed using alarge substrate. In addition, since the transistor can be formed withoutusing a mask (a reticle), a layout of the transistor can be easilychanged. Further, since it is not necessary to use a resist, materialcost is reduced and the number of steps can be reduced. Furthermore,since a film is formed only in a necessary portion, a material is notwasted compared with a manufacturing method in which etching isperformed after the film is formed over the entire surface, so that costcan be reduced.

A transistor including an organic semiconductor or a carbon nanotube, orthe like can be used. Accordingly, such a transistor can be formed usinga substrate which can be bent. Therefore, a device using a transistorincluding an organic semiconductor or a carbon nanotube, or the like canresist a shock.

Further, transistors with various structures can be used. For example, aMOS transistor, a junction transistor, a bipolar transistor, or the likecan be used as a transistor. When a MOS transistor is used, the size ofthe transistor can be reduced. Thus, a large number of transistors canbe mounted. When a bipolar transistor is used, large current can flow.Thus, a circuit can be operated at high speed.

Note that a MOS transistor, a bipolar transistor, and the like may beformed over one substrate. Thus, reduction in power consumption,reduction in size, high speed operation, and the like can be realized.

Furthermore, various transistors can be used.

Note that a transistor can be formed using various types of substrateswithout limiting to a certain type. For example, a single-crystalsubstrate, an SOI substrate, a glass substrate, a quartz substrate, aplastic substrate, a paper substrate, a cellophane substrate, a stonesubstrate, a wood substrate, a cloth substrate (including a naturalfiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon,polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra,rayon, or regenerated polyester), or the like), a leather substrate, arubber substrate, a stainless steel substrate, a substrate including astainless steel foil, or the like can be used as a substrate over whicha transistor is formed. Alternatively, a skin (e.g., epidermis orcorium) or hypodermal tissue of an animal such as a human being can beused as a substrate. Further alternatively, the transistor may be formedusing one substrate, and then, the transistor may be transferred toanother substrate, and the transistor may be provided over anothersubstrate. A single-crystal substrate, an SOI substrate, a glasssubstrate, a quartz substrate, a plastic substrate, a paper substrate, acellophane substrate, a stone substrate, a wood substrate, a clothsubstrate (including a natural fiber (e.g., silk, cotton, or hemp), asynthetic fiber (e.g., nylon, polyurethane, or polyester), a regeneratedfiber (e.g., acetate, cupra, rayon, or regenerated polyester), or thelike), a leather substrate, a rubber substrate, a stainless steelsubstrate, a substrate including a stainless steel foil, or the like canbe used as a substrate to which the transistor is transferred.Alternatively, a skin (e.g., epidermis or corium) or hypodermal tissueof an animal such as a human being can be used as a substrate. Furtheralternatively, the transistor may be formed using one substrate and thesubstrate may be thinned by polishing. A single-crystal substrate, anSOI substrate, a glass substrate, a quartz substrate, a plasticsubstrate, a paper substrate, a cellophane substrate, a stone substrate,a wood substrate, a cloth substrate (including a natural fiber (e.g.,silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, orpolyester), a regenerated fiber (e.g., acetate, cupra, rayon, orregenerated polyester), or the like), a leather substrate, a rubbersubstrate, a stainless steel substrate, a substrate including astainless steel foil, or the like can be used as a substrate.Alternatively, a skin (e.g., epidermis or corium) or hypodermal tissueof an animal such as a human being can be used as a substrate to bepolished. When such a substrate is used, a transistor with excellentproperties or a transistor with low power consumption can be formed, adevice with high durability, high heat resistance can be provided, orreduction in weight or thickness can be achieved.

Note that a structure of a transistor can be various modes withoutlimiting to a certain structure. For example, a multi-gate structurehaving two or more gate electrodes may be used. When the multi-gatestructure is used, a structure where a plurality of transistors areconnected in series is provided because channel regions are connected inseries. With the multi-gate structure, off-current can be reduced or thewithstand voltage of the transistor can be increased to improvereliability. Alternatively, with the multi-gate structure, drain-sourcecurrent does not fluctuate very much even if drain-source voltagefluctuates when the transistor operates in a saturation region, so thata flat slope of voltage-current characteristics can be obtained. Whenthe flat slope of the voltage-current characteristics is utilized, anideal current source circuit or an active load having an extremely highresistance value can be realized. Accordingly, a differential circuit ora current mirror circuit having excellent properties can be realized.

In addition, a structure where gate electrodes are formed above andbelow a channel may be used. When the structure where gate electrodesare formed above and below the channel is used, a channel region isincreased, so that the amount of current flowing therethrough can beincreased or a depletion layer can be easily formed to decreasesubthreshold swing. When the gate electrodes are formed above and belowthe channel, a structure where a plurality of transistors are connectedin parallel is provided.

Alternatively, a structure where a gate electrode is formed above achannel region, a structure where a gate electrode is formed below achannel region, a staggered structure, an inversely staggered structure,a structure where a channel region is divided into a plurality ofregions, or a structure where channel regions are connected in parallelor in series can be used. Further alternatively, a source electrode or adrain electrode may overlap with a channel region (or part of it). Whenthe structure where the source electrode or the drain electrode mayoverlap with the channel region (or part of it) is used, the case can beprevented in which electric charges are accumulated in part of thechannel region, which would result in an unstable operation. Furtheralternatively, an LDD region may be provided. When the LDD region isprovided, off-current can be reduced or the withstand voltage of thetransistor can be increased to improve reliability. Further, when theLDD region is provided, drain-source current does not fluctuate verymuch even if drain-source voltage fluctuates when the transistoroperates in the saturation region, so that a flat slope ofvoltage-current characteristics can be obtained.

Note that various types of transistors can be used as a transistor andthe transistor can be formed using various types of substrates.Accordingly, all the circuits that are necessary to realize apredetermined function can be formed using the same substrate. Forexample, all the circuits that are necessary to realize thepredetermined function can be formed using a glass substrate, a plasticsubstrate, a single-crystal substrate, an SOI substrate, or any othersubstrate. When all the circuits that are necessary to realize thepredetermined function are formed using the same substrate, cost can bereduced by reduction in the number of component parts or reliability canbe improved by reduction in the number of connections to circuitcomponents. Alternatively, part of the circuits which are necessary torealize the predetermined function can be formed using one substrate andanother part of the circuits which are necessary to realize thepredetermined function can be formed using another substrate. That is,not all the circuits that are necessary to realize the predeterminedfunction are required to be formed using the same substrate. Forexample, part of the circuits which are necessary to realize thepredetermined function may be formed by transistors using a glasssubstrate and another part of the circuits which are necessary torealize the predetermined function may be formed using a single-crystalsubstrate, so that an IC chip formed by a transistor over thesingle-crystal substrate can be connected to the glass substrate by COG(chip on glass) and the IC chip may be provided over the glasssubstrate. Alternatively, the IC chip can be connected to the glasssubstrate by TAB (tape automated bonding) or a printed wiring board.When part of the circuits are formed using the same substrate in thismanner, cost can be reduced by reduction in the number of componentparts or reliability can be improved by reduction in the number ofconnections to circuit components. Further alternatively, when circuitswith high driving voltage and high driving frequency, which consumelarge power, are formed over a single-crystal semiconductor substrateinstead of forming such circuits using the same substrate and an IC chipformed by the circuit is used, increase in power consumption can beprevented.

Note that one pixel corresponds to one element whose brightness can becontrolled. Therefore, for example, one pixel corresponds to one colorelement and brightness is expressed with the one color element.Accordingly, in the case of a color display device having color elementsof R (red), G (green), and B (blue), a minimum unit of an image isformed of three pixels of an R pixel, a G pixel, and a B pixel. Notethat the color elements are not limited to three colors, and colorelements of more than three colors may be used or a color other than RGBmay be used. For example, RGBW (W corresponds to white) can be used byadding white. Alternatively, one or more colors of yellow, cyan, magentaemerald green, vermilion, and the like can be added to RGB. Furtheralternatively, a color similar to at least one of R, G, and B can beadded to RGB. For example, R, G, B1, and B2 may be used. Although bothB1 and B2 are blue, they have slightly different frequency. Similarly,R1, R2, G, and B can be used. When such color elements are used, displaywhich is closer to the real object can be performed and powerconsumption can be reduced. As another example, in the case ofcontrolling brightness of one color element by using a plurality ofregions, one region can correspond to one pixel. Therefore, for example,in the case of performing area ratio gray scale display or the case ofincluding a subpixel, a plurality of regions which control brightnessare provided in each color element and gray scales are expressed withthe whole regions. In this case, one region which controls brightnessmay correspond to one pixel. Thus, in that case, one color elementincludes a plurality of pixels. Alternatively, even when the pluralityof regions which control brightness are provided in one color element,these regions may be collected as one pixel. Thus, in that case, onecolor element includes one pixel. In that case, one color elementincludes one pixel. Further alternatively, in the case where brightnessis controlled in a plurality of regions in each color element, regionswhich contribute to display have different area dimensions depending onpixels in some cases. Further alternatively, in the plurality of regionswhich control brightness in each color element, signals supplied to eachof the plurality of regions may be slightly varied to widen a viewingangle. That is, potentials of pixel electrodes included in the pluralityof regions provided in each color element can be different from eachother. Accordingly, voltage applied to liquid crystal molecules arevaried depending on the pixel electrodes. Therefore, the viewing anglecan be widened.

Note that explicit description “one pixel (for three colors)”corresponds to the case where three pixels of R, G, and B are consideredas one pixel. Meanwhile, explicit description “one pixel (for onecolor)” corresponds to the case where the plurality of regions areprovided in each color element and collectively considered as one pixel.

Note that pixels are provided (arranged) in matrix in some cases. Here,description that pixels are provided (arranged) in matrix includes thecase where the pixels are arranged in a straight line or the case wherethe pixels are arranged in a jagged line, in a longitudinal direction ora lateral direction. Thus, for example, in the case of performing fullcolor display with three color elements (e.g., RGB), the following casesare included therein: the case where the pixels are arranged in stripesor the case where dots of the three color elements are arranged in adelta pattern. Alternatively, the case is also included therein in whichdots of the three color elements are provided in Bayer arrangement. Notethat the color elements are not limited to three colors, and colorelements of more than three colors may be used. For example, RGBW (Wcorresponds to white), RGB plus one or more of yellow, cyan, magenta, orthe like may be used. Note that the sizes of display regions may bedifferent between respective dots of color elements. Thus, powerconsumption can be reduced or the life of a display element can beprolonged.

Note that an active matrix method in which an active element is includedin a pixel or a passive matrix method in which an active element is notincluded in a pixel can be used.

In an active matrix method, as an active element (a non-linear element),not only a transistor but also various active elements (non-linearelements) can be used. For example, an MIM (metal insulator metal), aTFD (thin film diode), or the like can also be used. Since such anelement has few numbers of manufacturing steps, manufacturing cost canbe reduced or yield can be improved. Further, since the size of theelement is small, the aperture ratio can be improved, so that powerconsumption can be reduced or high luminance can be achieved.

Note that as a method other than an active matrix method, a passivematrix method in which an active element (a non-linear element) is notused can also be used. Since an active element (a non-linear element) isnot used, manufacturing steps is few, so that manufacturing cost can bereduced or the yield can be improved. Since an active element (anon-linear element) is not used, the aperture ratio can be improved, sothat power consumption can be reduced or high luminance can be achieved.

Note that a transistor is an element having at least three terminals ofa gate, a drain, and a source. The transistor has a channel regionbetween a drain region and a source region, and current can flow throughthe drain region, the channel region, and the source region. Here, sincethe source and the drain of the transistor change depending on thestructure, the operating condition, and the like of the transistor, itis difficult to define which is a source or a drain. Therefore, in thisdocument (the specification, the claim, the drawing, and the like), aregion functioning as a source and a drain may not be called the sourceor the drain. In such a case, one of the source and the drain may bereferred to as a first terminal and the other thereof may be referred toas a second terminal, for example. Alternatively, one of the source andthe drain may be referred to as a first electrode and the other thereofmay be referred to as a second electrode. Further alternatively, one ofthe source and the drain may be referred to as a source region and theother thereof may be called a drain region.

Note that a transistor may be an element having at least three terminalsof a base, an emitter, and a collector. In this case, one of the emitterand the collector may be similarly referred to as a first terminal andthe other terminal may be referred to as a second terminal.

Note that a gate corresponds to all or part of a gate electrode and agate wiring (also referred to as a gate line, a gate signal line, a scanline, a scan signal line, or the like). A gate electrode corresponds toa conductive film which overlaps with a semiconductor which forms achannel region with a gate insulating film interposed therebetween. Notethat part of the gate electrode overlaps with an LDD (lightly dopeddrain) region or the source region (or the drain region) with the gateinsulating film interposed therebetween in some cases. A gate wiringcorresponds to a wiring for connecting a gate electrode of eachtransistor to each other, a wiring for connecting a gate electrode ofeach pixel to each other, or a wiring for connecting a gate electrode toanother wiring.

However, there is a portion (a region, a conductive film, a wiring, orthe like) which functions as both a gate electrode and a gate wiring.Such a portion (a region, a conductive film, a wiring, or the like) maybe referred to as either a gate electrode or a gate wiring. That is,there is a region where a gate electrode and a gate wiring cannot beclearly distinguished from each other. For example, in the case where achannel region overlaps with part of an extended gate wiring, theoverlapped portion (region, conductive film, wiring, or the like)functions as both a gate wiring and a gate electrode. Accordingly, sucha portion (a region, a conductive film, a wiring, or the like) may bereferred to as either a gate electrode or a gate wiring.

Note that a portion (a region, a conductive film, a wiring, or the like)which is formed using the same material as a gate electrode, forms thesame island as the gate electrode, and is connected to the gateelectrode may also be referred to as a gate electrode. Similarly, aportion (a region, a conductive film, a wiring, or the like) which isformed using the same material as a gate wiring, forms the same islandas the gate wiring, and is connected to the gate wiring may also bereferred to as a gate wiring. In a strict detect, such a portion (aregion, a conductive film, a wiring, or the like) does not overlap witha channel region or does not have a function of connecting the gateelectrode to another gate electrode in some cases. However, there is aportion (a region, a conductive film, a wiring, or the like) which isformed using the same material as a gate electrode or a gate wiring,forms the same island as the gate electrode or the gate wiring, and isconnected to the gate electrode or the gate wiring because ofspecifications or the like in manufacturing. Thus, such a portion (aregion, a conductive film, a wiring, or the like) may also be referredto as either a gate electrode or a gate wiring.

Note that in a multi-gate transistor, for example, a gate electrode isoften connected to another gate electrode by using a conductive filmwhich is formed using the same material as the gate electrode. Sincesuch a portion (a region, a conductive film, a wiring, or the like) is aportion (a region, a conductive film, a wiring, or the like) forconnecting the gate electrode to another gate electrode, it may bereferred to as a gate wiring, and it may also be referred to as a gateelectrode because a multi-gate transistor can be considered as onetransistor. That is, a portion (a region, a conductive film, a wiring,or the like) which is formed using the same material as a gate electrodeor a gate wiring, forms the same island as the gate electrode or thegate wiring, and is connected to the gate electrode or the gate wiringmay be referred to as either a gate electrode or a gate wiring. Inaddition, for example, part of a conductive film which connects the gateelectrode and the gate wiring and is formed using a material which isdifferent from that of the gate electrode or the gate wiring may also bereferred to as either a gate electrode or a gate wiring.

Note that a gate terminal corresponds to part of a portion (a region, aconductive film, a wiring, or the like) of a gate electrode or a portion(a region, a conductive film, a wiring, or the like) which iselectrically connected to the gate electrode.

Note that when a wiring is referred to as a gate wiring, a gate line, agate signal line, a scan line, a scan signal line, there is the case inwhich a gate of a transistor is not connected to a wiring. In this case,the gate wiring, the gate line, the gate signal line, the scan line, orthe scan signal line corresponds to a wiring formed in the same layer asthe gate of the transistor, a wiring formed using the same material ofthe gate of the transistor, or a wiring formed at the same time as thegate of the transistor in some cases. As examples, there are a wiringfor a storage capacitor, a power supply line, a reference potentialsupply line, and the like.

Note that a source corresponds to all or part of a source region, asource electrode, and a source wiring (also referred to as a sourceline, a source signal line, a data line, a data signal line, or thelike). A source region corresponds to a semiconductor region including alarge amount of p-type impurities (e.g., boron or gallium) or n-typeimpurities (e.g., phosphorus or arsenic). Therefore, a region includinga small amount of p-type impurities or n-type impurities, namely, an LDD(lightly doped drain) region is not included in the source region. Asource electrode is part of a conductive layer which is formed using amaterial different from that of a source region and is electricallyconnected to the source region. However, there is the case where asource electrode and a source region are collectively referred to as asource electrode. A source wiring is a wiring for connecting a sourceelectrode of each transistor to each other, a wiring for connecting asource electrode of each pixel to each other, or a wiring for connectinga source electrode to another wiring.

However, there is a portion (a region, a conductive film, a wiring, orthe like) functioning as both a source electrode and a source wiring.Such a portion (a region, a conductive film, a wiring, or the like) maybe referred to as either a source electrode or a source wiring. That is,there is a region where a source electrode and a source wiring cannot beclearly distinguished from each other. For example, in the case where asource region overlaps with part of an extended source wiring, theoverlapped portion (region, conductive film, wiring, or the like)functions as both a source wiring and a source electrode. Accordingly,such a portion (a region, a conductive film, a wiring, or the like) maybe referred to as either a source electrode or a source wiring.

Note that a portion (a region, a conductive film, a wiring, or the like)which is formed using the same material as a source electrode, forms thesame island as the source electrode, and is connected to the sourceelectrode, or a portion (a region, a conductive film, a wiring, or thelike) which connects a source electrode and another source electrode mayalso be referred to as a source electrode. Further, a portion whichoverlaps with a source region may be referred to as a source electrode.Similarly, a portion (a region, a conductive film, a wiring, or thelike) which is formed using the same material as a source wiring, formsthe same island as the source wiring, and is connected to the sourcewiring may also be referred to as a source wiring. In a strict sense,such a portion (a region, a conductive film, a wiring, or the like) doesnot have a function of connecting the source electrode to another sourceelectrode in some cases. However, there is a portion (a region, aconductive film, a wiring, or the like) which is formed using the samematerial as a source electrode or a source wiring, forms the same islandas the source electrode or the source wiring, and is connected to thesource electrode or the source wiring because of specifications or thelike in manufacturing. Thus, such a portion (a region, a conductivefilm, a wiring, or the like) may also be referred to as either a sourceelectrode or a source wiring.

For example, part of a conductive film which connects a source electrodeand a source wiring and is formed using a material which is differentfrom that of the source electrode or the source wiring may be referredto as either a source electrode or a source wiring.

Note that a source terminal corresponds to part of a source region, asource electrode, or a portion (a region, a conductive film, a wiring,or the like) which is electrically connected to the source electrode.

Note that when a wiring is referred to as a source wiring, a sourceline, a source signal line, a data line, a data signal line, there isthe case in which a source (a drain) of a transistor is not connected toa wiring. In this case, the source wiring, the source line, the sourcesignal line, the data line, or the data signal line corresponds to awiring formed in the same layer as the source (the drain) of thetransistor, a wiring formed using the same material of the source (thedrain) of the transistor, or a wiring formed at the same time as thesource (the drain) of the transistor in some cases. As examples, thereare a wiring for a storage capacitor, a power supply line, a referencepotential supply line, and the like.

Note that the same can be said for a drain.

Note that a semiconductor device corresponds to a device having acircuit including a semiconductor element (e.g., a transistor, a diode,or a thyristor). The semiconductor device may also include all devicesthat can function by utilizing semiconductor characteristics. Inaddition, the semiconductor device corresponds to a device having asemiconductor material.

Note that a display element corresponds to an optical modulationelement, a liquid crystal element, a light-emitting element, an ELelement (an organic EL element, an inorganic EL element, or an ELelement including organic and inorganic materials), an electron emitter,an electrophoresis element, a discharging element, a light-reflectiveelement, a light diffraction element, a digital micromirror device(DMD), or the like. Note that the present invention is not limited tothis.

Note that a display device corresponds to a device having a displayelement. The display device may include a plurality of pixels eachhaving a display element. Note that that the display device may alsoinclude a peripheral driver circuit for driving the plurality of pixels.The peripheral driver circuit for driving the plurality of pixels may beformed over the same substrate as the plurality of pixels. The displaydevice may also include a peripheral driver circuit provided over asubstrate by wire bonding or bump bonding, namely, an IC chip connectedby chip on glass (COG) or an IC chip connected by TAB or the like.Further, the display device may also include a flexible printed circuit(FPC) to which an IC chip, a resistor, a capacitor, an inductor, atransistor, or the like is attached. Note also that the display deviceincludes a printed wiring board (PWB) which is connected through aflexible printed circuit (FPC) and to which an IC chip, a resistor, acapacitor, an inductor, a transistor, or the like is attached. Thedisplay device may also include an optical sheet such as a polarizingplate or a retardation plate. The display device may also include alighting device, a housing, an audio input and output device, a lightsensor, or the like. Here, a lighting device such as a backlight unitmay include a light guide plate, a prism sheet, a diffusion sheet, areflective sheet, a light source (e.g., an LED or a cold cathodefluorescent lamp), a cooling device (e.g., a water cooling device or anair cooling device), or the like.

Note that a lighting device corresponds to a device having a backlightunit, a light guide plate, a prism sheet, a diffusion sheet, areflective sheet, or a light source (e.g., an LED, a cold cathodefluorescent lamp, or a hot cathode fluorescent lamp), a cooling device,or the like.

Note that a light-emitting device corresponds to a device having alight-emitting element and the like. In the case of including alight-emitting element as a display element, the light-emitting deviceis one of specific examples of a display device.

Note that a reflective device corresponds to a device having alight-reflective element, a light diffraction element, light-reflectiveelectrode, or the like.

Note that a liquid crystal display device corresponds to a displaydevice including a liquid crystal element. Liquid crystal displaydevices include a direct-view liquid crystal display, a projectionliquid crystal display, a transmissive liquid crystal display, areflective liquid crystal display, a transflective liquid crystaldisplay, and the like.

Note that a driving device corresponds to a device having asemiconductor element, an electric circuit, or an electronic circuit.For example, a transistor which controls input of a signal from a sourcesignal line to a pixel (also referred to as a selection transistor, aswitching transistor, or the like), a transistor which supplies voltageor current to a pixel electrode, a transistor which supplies voltage orcurrent to a light-emitting element, and the like are examples of thedriving device. A circuit which supplies a signal to a gate signal line(also referred to as a gate driver, a gate line driver circuit, or thelike), a circuit which supplies a signal to a source signal line (alsoreferred to as a source driver, a source line driver circuit, or thelike) are also examples of the driving device.

Note that a display device, a semiconductor device, a lighting device, acooling device, a light-emitting device, a reflective device, a drivingdevice, and the like overlap with each other in some cases. For example,a display device includes a semiconductor device and a light-emittingdevice in some cases. Alternatively, a semiconductor device includes adisplay device and a driving device in some cases.

Note that when it is explicitly described that “B is formed on A” or “Bis formed over A”, it does not necessarily mean that B is formed indirect contact with A. The description includes the case where A and Bare not in direct contact with each other, i.e., the case where anotherobject is interposed between A and B. Here, each of A and B correspondsto an object (e.g., a device, an element, a circuit, a wiring, anelectrode, a terminal, a conductive film, or a layer).

Accordingly, for example, when it is explicitly described that “a layerB is formed on (or over) a layer A”, it includes both the case where thelayer B is formed in direct contact with the layer A, and the case whereanother layer (e.g., a layer C or a layer D) is formed in direct contactwith the layer A and the layer B is formed in direct contact with thelayer C or D. Note that another layer (e.g., a layer C or a layer D) maybe a single layer or a plurality of layers.

Similarly, when it is explicitly described that “B is formed above A”,it does not necessarily mean that B is formed in direct contact with A,and another object may be interposed therebetween. Thus, for example,when it is described that “a layer B is formed above a layer A”, itincludes both the case where the layer B is formed in direct contactwith the layer A, and the case where another layer (e.g., a layer C or alayer D) is formed in direct contact with the layer A and the layer B isformed in direct contact with the layer C or D. Note that another layer(e.g., a layer C or a layer D) may be a single layer or a plurality oflayers.

Note that when it is explicitly described that “B is formed in directcontact with A”, it includes not the case where another object isinterposed between A and B but the case where B is formed in directcontact with A.

Note that the same can be said when it is described that B is formedbelow or under A.

Note that when an object is explicitly described in a singular form, theobject is preferably singular. Note that the present invention is notlimited to this, and the object can be plural. Similarly, when an objectis explicitly described in a plural form, the object is preferablyplural. Note that the present invention is not limited to this, and theobject can be singular.

A semiconductor device can be manufactured with low cost. Alternatively,a multifunctional semiconductor device can be provided. Alternatively, asemiconductor device provided with a circuit which can operate at highspeed can be provided. Alternatively, a semiconductor device whichconsumes low power can be provided. Alternatively, a semiconductordevice of which manufacturing steps are reduced can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D illustrate manufacturing steps of a semiconductor deviceof the present invention;

FIGS. 2A to 2D illustrate manufacturing steps of a semiconductor deviceof the present invention;

FIGS. 3A to 3C illustrate manufacturing steps of a semiconductor deviceof the present invention;

FIGS. 4A and 4B illustrate manufacturing steps of a semiconductor deviceof the present invention;

FIG. 5 illustrates a manufacturing step of a semiconductor device of thepresent invention;

FIG. 6 illustrates a manufacturing step of a semiconductor device of thepresent invention;

FIG. 7 illustrates a cross-sectional view of a semiconductor device ofthe present invention;

FIG. 8 illustrates a cross-sectional view of a semiconductor device ofthe present invention;

FIG. 9 illustrates a cross-sectional view of a semiconductor device ofthe present invention;

FIG. 10 illustrates a cross-sectional view of a semiconductor device ofthe present invention;

FIG. 11 illustrates a top view of a semiconductor device of the presentinvention;

FIGS. 12A and 12B illustrate cross-sectional views of an SOI substrateof the present invention;

FIGS. 13A and 13B illustrate cross-sectional views of an SOI substrateof the present invention;

FIGS. 14A to 14C illustrate cross-sectional views of an SOI substrate ofthe present invention;

FIG. 15 illustrates a cross-sectional view of an SOI substrate of thepresent invention;

FIGS. 16A to 16C illustrate cross-sectional views of an SOI substrate ofthe present invention;

FIG. 17 illustrates a cross-sectional view of a liquid crystal displaydevice of present invention;

FIGS. 18A to 18D illustrate cross-sectional views of a liquid crystaldisplay device of present invention;

FIG. 19 illustrates a cross-sectional view of a liquid crystal displaydevice of present invention;

FIGS. 20A to 20C illustrate a structure of a liquid crystal displaydevice of present invention;

FIG. 21 illustrates a cross-sectional view of a liquid crystal displaydevice of present invention;

FIGS. 22A and 22B illustrate circuit diagrams of a pixel of the presentinvention;

FIG. 23 illustrates a circuit diagram of pixels of the presentinvention;

FIG. 24 illustrates a circuit diagram of pixels of the presentinvention;

FIGS. 25A and 25B illustrate a top view and a cross-sectional view of apixel of the present invention;

FIG. 26 illustrates an electronic device of the present invention;

FIG. 27 illustrates an electronic device of the present invention;

FIGS. 28A and 28B illustrate electronic devices of the presentinvention;

FIG. 29 illustrates an electronic device of the present invention;

FIGS. 30A to 30C illustrate electronic devices of the present invention;

FIG. 31 illustrates an electronic device of the present invention;

FIG. 32 illustrates an electronic device of the present invention;

FIG. 33 illustrates an electronic device of the present invention;

FIG. 34 illustrates an electronic device of the present invention;

FIGS. 35A and 35B illustrate electronic devices of the presentinvention;

FIGS. 36A and 36B illustrate an electronic device of the presentinvention;

FIGS. 37A to 37C illustrate electronic devices of the present invention;

FIGS. 38A and 38B illustrate electronic devices of the presentinvention; and

FIG. 39 illustrates an electronic device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Modes

Embodiment Modes of the present invention will be hereinafter describedin detail with reference to the accompanying drawings. However, it iseasily understood by those skilled in the art that the present inventioncan be implemented in various different modes, and modes and details ofthe present invention can be modified in various ways without departingfrom the purpose and the scope of the present invention. Accordingly,the present invention should not be interpreted as being limited to thedescription of the embodiment modes. Note that in structures of thepresent invention described below, reference numerals denoting the samecomponents are used in common in different drawings, and detaileddescription of the same portions or portions having similar functions isomitted.

Embodiment Mode 1

All or a part of a semiconductor device or a display device includes aTFT which is formed over a glass substrate in such manner that a siliconlayer is separated from a single-crystal substrate and bonded(transferred) to the glass substrate, or a TFT formed over a glasssubstrate in such a manner that a single-crystal substrate is bonded tothe glass substrate and separated from the glass substrate to form asilicon layer over the glass substrate. Not that the TFTs which isformed over a glass substrate in such manner that a silicon layer isseparated from a single-crystal substrate and transferred to the glasssubstrate, or a TFT formed over a glass substrate in such a manner thata single-crystal substrate is bonded to a glass substrate and separatedfrom the glass substrate to transfer a silicon layer which is part ofthe silicon substrate over the glass substrate are hereinafter referredto as single-crystal TFT.

Then, a non-single-crystal TFT is also formed at the same time as asingle-crystal TFT. Examples of a non-single-crystal includes anamorphous semiconductor, a micro-crystal semiconductor (also referred toas a microcrystalline semiconductor, a semi-amorphous semiconductor, anda nanocrystal semiconductor).

Next, a manufacturing method is described with reference to drawings.

As shown in FIG. 1A, various substrates can be used for an insulatingsubstrate 101 without limiting to a glass substrate. For example, aglass substrate such as a barium borosilicate glass, analuminoborosilicate glass, a quartz substrate, a ceramic substrate, or ametal substrate including stainless steel can be used. Further, asubstrate formed of plastics typified by polyethylene terephthalate(PET), polyethylene naphthalate (PEN), or polyethersulfone (PES), or asubstrate formed of a flexible synthetic resin such as acrylic can alsobe used. By using a flexible substrate, a bendable semiconductor devicecan be manufactured. Since a flexible substrate has no restrictions onthe area and the shape, a rectangular substrate with a side of one meteror more can be used as the insulating substrate 101, for example, sothat productivity can be significantly improved. Such merit is greatlyadvantageous as compared to a case of using a round silicon substrate.

Note that it is preferable that an insulating film be provided over thesurface of the insulating substrate 101. The insulating film serves as abase film. That is, the insulating film is provided in order to preventalkali metal such as Na or alkaline earth metals from the inside of theinsulating substrate 101 from affecting characteristics of thesemiconductor device adversely. The insulating film can have asingle-layer structure or a stacked-layer structure of insulating filmscontaining oxygen or nitrogen, such as silicon oxide (SiO_(x)), siliconnitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y), x>y), or siliconnitride oxide (SiN_(x)O_(y), x>y). In the case where the insulating filmhas a two-layer structure, it is preferable that a silicon nitride oxidefilm be formed for a first layer, and a silicon oxynitride film beformed for a second layer, for example. As another example, in the casewhere the insulating film has a three-layer structure, it is preferablethat a silicon oxynitride film be used as a first insulating film, asilicon nitride oxide film be used as a second insulating film, and asilicon oxynitride film be used as a third insulating film.

However, it is also possible that the insulating film is not providedover the surface of the insulating substrate 101 without limiting tothis.

Then, a semiconductor layer 102 is provided over the insulatingsubstrate 101 which is provided with an insulating film, or the like.The semiconductor layer 102 may be provided over the entire surface orpart of the surface of the insulating substrate 101. The semiconductorlayer 102 is preferably single-crystal. However, the present inventionis not limited to this. Single-crystal is preferable for an excellentcurrent characteristic and high mobility.

Note that an arranging method of the semiconductor layer 102, or thelike will be described in a different embodiment mode.

Next as shown in FIG. 1B, an unnecessary portion of the semiconductorlayer 102 is removed by etching so that the semiconductor layer 102 hasa predetermined shape. That is, the semiconductor layer 102 is processedinto the island shape. In other words, the semiconductor layer 102 ispatterned.

The semiconductor layer 102 serves as an active layer of a transistor.However, the semiconductor layer 102 can serves as an electrode of acapacitor element, a resistor element, an active layer of a diode, orthe like in some cases without being limited to this.

Next as shown in FIG. 1C, an insulating layer 103 is provided so as tocover the semiconductor layer 102. The insulating layer 103 is providedusing a CVD method, a sputtering method, a thermal oxidation method, avapor deposition method, an ink jet method, a printing method, or thelike. The insulating layer 103 also serves as a gate insulating film.Alternatively, the insulating layer 103 serves as an insulator of acapacitor element or an interlayer film in some cases.

The insulating layer 103 can be formed by a single-layer structure or astacked-layer structure of a siloxane resin; a film, of silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y))(x>y), silicon nitride oxide (SiN_(x)O_(y)) (x>y), or the like; a filmcontaining carbon, such as a DLC (diamond-like carbon); an organicmaterial such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; or an insulating film containing oxygen ornitrogen. Note that a siloxane resin corresponds to a resin havingSi—O—Si bonds. Siloxane includes a skeleton structure of a bond ofsilicon (Si) and oxygen (O). As a substituent, an organic groupcontaining at least hydrogen (such as an alkyl group or aromatichydrocarbon) is used. Alternatively, a fluoro group, or a fluoro groupand an organic group containing at least hydrogen can be used as asubstituent.

A portion of the insulating layer 103 in contact with the semiconductorlayer 102 is preferably silicon oxide (SiO_(x)). A phenomenon of anelectron being trapped or hysteresis effect can be prevented by usingsilicon oxide (SiO_(x)).

Next as shown in FIG. 1D, a conductive layer 104 is provided so as tocover the insulating layer 103. The conductive layer 104 is providedusing a CVD method, a sputtering method, a thermal oxidation method, avapor deposition method, an ink jet method, a printing method, or thelike.

Next as shown in FIG. 2A, an unnecessary portion of the conductive layer104 is removed by etching so that the conductive layer 104 has apredetermined shape. That is, the conductive layer 104 is processed intothe island shape. In other words, the conductive layer 104 is patterned.As a result, a gate electrode 104A and a gate electrode 104B are formed.

The gate electrode 104A forms a transistor 203 together with thesemiconductor layer 102 and the insulating layer 103. Since the gateelectrode 104A is provided over the semiconductor layer 102, thetransistor 203 is a top gate transistor.

Note that, the transistor 203 can have various structures. For example,the transistor 203 can be a single drain transistor. In this case, sincethe transistor 203 can be formed in a simple method, there areadvantages of low manufacturing cost and high yield. Here, thesemiconductor layer 102 has regions of different concentrations of animpurity, a channel formation region, a source region, and a drainregion. By controlling the concentration of impurities in this manner,resistivity of the semiconductor layer can be controlled. In the sourceregion and a drain region, an electrical connection state of thesemiconductor layer 102 and the conductive film can be closer to ohmiccontact. Note that as a method of forming the semiconductor layers eachhaving different amount of impurities as selected, a method can be usedin which the semiconductor layer is doped with an impurity using thegate electrode 104A as a mask.

Alternatively, in the transistor 203, the gate electrode 104A can betapered at least certain degrees. In this case, since the transistor 203can be formed in a simple method, there are advantages of lowmanufacturing cost and high yield. Here, the semiconductor layer 102 hasregions of different concentrations of an impurity, a channel formationregion, lightly doped drain (LDD) region, a source region and a drainregion. By controlling the amount of impurities in this manner,resistivity of the semiconductor layer can be controlled. An electricalconnection state of the semiconductor layer 102 and the conductive filmconnected thereto can be closer to ohmic contact. Moreover, since thetransistor includes the LDD region, a high electric field is not easilyapplied to inside of the transistor, so that deterioration of theelement due to hot carriers can be suppressed. Note that as a method offorming the semiconductor layers each including a different amount of animpurity as selected, a method where impurities are added to thesemiconductor layer using the gate electrode 104A as a mask can be used.If the gate electrode 104A is tapered at more than certain degrees, theimpurity can be added to the semiconductor layer through the gateelectrode 104A with a gradient so that the LDD region can be easilyformed.

Alternatively, the transistor 203 can have the gate electrode 104Aformed of at least two layers, and a lower gate electrode can be longerthan an upper gate electrode. In this case, a shape of the lower andupper gate electrodes can be called a hat shape. When the gate electrode104A has a hat shape, an LDD region can be formed without addition of aphotomask. Note that a structure where the LDD region overlaps with thegate electrode 104A is particularly called a GOLD (gate overlapped LDD)structure. As a method of forming the gate electrode 104A with a hatshape, the following method may be used.

First, when the gate electrode 104A is patterned, the lower and uppergate electrodes are etched by dry etching so that side surfaces thereofare inclined (tapered). Then, an inclination of the upper gate electrodeis processed to be almost perpendicular by anisotropic etching. Thus,the gate electrode is formed such that the cross section is hat-shaped.After that, a channel region, an LDD region, a source region, and adrain region are formed by the semiconductor layer with an impurityelement twice.

Note that a portion of the LDD region which overlaps with the gateelectrode 104A is referred to as an Lov region, and a portion of the LDDregion which does not overlap with the gate electrode 104A is referredto as an Loff region. The Loff region is highly effective in suppressingan off-current value, whereas it is not very effective in preventingdeterioration in an on-current value due to hot carriers by relieving anelectric field in the vicinity of the drain. On the other hand, the Lovregion works effectively in preventing deterioration in the on-currentvalue by relieving the electric field in the vicinity of the drain;however, it does not work effectively in suppressing the off-currentvalue. Thus, it is preferable to form a transistor having a structurecorresponding to characteristics required for each of the variouscircuits. For example, when the semiconductor device is used for adisplay device, a transistor having a Loff region is preferably used asa pixel transistor in order to suppress the off-current value. On theother hand, as a transistor in a peripheral circuit, a transistor havingan Lov region is preferably used in order to prevent deterioration inthe on-current value by relieving the electric field in the vicinity ofthe drain.

Alternatively, the transistor 203 can include sidewalls in contact withthe side portion of the gate electrode 104A. When the transistorincludes the sidewall, a region overlapping with the sidewall can bemade to be an LDD region.

Alternatively, in the transistor 203, the semiconductor layer 102 can bedoped using a mask so that an LDD (Loff) region can be formed. Thus, theLDD region can surely be formed, and an off-current value of thetransistor can be reduced.

Alternatively, in the transistor 203, the semiconductor layer can bedoped using a mask so that an LDD (Lov) region can be formed. Thus, theLDD region can surely be formed, and deterioration in an on-currentvalue can be prevented by relieving the electric field in the vicinityof the drain of the transistor.

Note that the conductive layer 104 can be processed into a conductivefilm having various functions without being limited to the gateelectrode. For example, various functions of the conductive film includea wiring or an electrode such as a wiring for forming a storagecapacitor, a wiring for forming a scan line, a wiring for connectingcircuits, or the like.

Next, as shown in FIG. 2B, an insulating layer 201 is provided so as tocover the gate electrode 104A and the gate electrode 104B. Theinsulating layer 201 is provided using a CVD method, a sputteringmethod, a thermal oxidation method, a vapor deposition method, an inkjet method, a printing method, or the like. The insulating layer 201serves as a gate insulating film. Alternatively, the insulating layer201 serves as an insulator of a capacitor element or an interlayer filmin some cases.

The insulating layer 201 can be formed by a single-layer structure or astacked-layer structure of a siloxane resin; a film, of silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y))(x>y), silicon nitride oxide (SiN_(x)O_(y)) (x>y), or the like; a filmcontaining carbon, such as a DLC (diamond-like carbon); an organicmaterial such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; or an insulating film containing oxygen ornitrogen. Note that a siloxane resin corresponds to a resin havingSi—O—Si bonds. Siloxane includes a skeleton structure of a bond ofsilicon (Si) and oxygen (O). As a substituent, an organic groupcontaining at least hydrogen (such as an alkyl group or aromatichydrocarbon) is used. Alternatively, a fluoro group, or a fluoro groupand an organic group containing at least hydrogen can be used as asubstituent.

It is preferable that a portion of the insulating layer 201 in contactwith a semiconductor layer 202, which is provided later, be siliconnitride (SiN_(x)). The semiconductor layer 202 includes hydrogen in somecase. In that case, reacting the hydrogen included in the semiconductorlayer 202 and the insulating layer 201 can be prevented by using siliconnitride (SiN_(x)) as the insulating layer 201.

Next, as shown in FIG. 2C, the semiconductor layer 202 is provided so asto cover the insulating layer 201. The semiconductor layer 202 isprovided using a CVD method, a sputtering method, a thermal oxidationmethod, a vapor deposition method, an ink jet method, a printing method,or the like. The semiconductor layer 202 includes at least two layers,and an impurity semiconductor is provided over an intrinsicsemiconductor.

The crystallinity of the semiconductor layer 202 is preferablyamorphous, micro-crystal (also referred to as microcrystal,semi-amorphous, nanocrystal, or the like).

Next as shown in FIG. 2D, an unnecessary portion of the semiconductorlayer 202 is removed by etching so that the semiconductor layer 202 hasa predetermined shape. That is, the semiconductor layer 202 is processedinto the island shape. In other words, the semiconductor layer 202 ispatterned.

In this case, the patterned semiconductor layer 202A serves as an activelayer of a transistor. However, the present invention is not limited tothis. The semiconductor layer can also serve as an interlayer film. Inother words, intersection capacitance of the wiring can be reduced byproviding a semiconductor layer, and disconnection of the wiring can bereduced by reducing a bumps. For example, a semiconductor layer 202B anda semiconductor layer 202C serve as interlayer films.

Next as shown in FIG. 3A, a conductive layer 301 is provided so as tocover the semiconductor layer 202A, the semiconductor layer 202B, andthe semiconductor layer 202C. The conductive layer 301 is provided usinga CVD method, a sputtering method, a thermal oxidation method, a vapordeposition method, an ink jet method, a printing method, or the like.

The conductive layer 104 and the conductive layer 301 can have asingle-layer structure of a conductive film or a stacked-layer structureof two or three conductive films. A conductive film can be used as amaterial of the conductive layer 104. For example, a single film of anelement such as tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten(W), chromium (Cr), silicon (Si), aluminum (Al), nickel (Ni), carbon(C), tungsten (W), platinum (Pt), copper (Cu), tantalum (Ta), gold (Au),or manganese (Mn); a nitride film of the aforementioned element(typically, a tantalum nitride film, a tungsten nitride film, or atitanium nitride film); an alloy film in which the aforementionedelements are combined (typically, a Mo—W alloy or a Mo—Ta alloy); asilicide film of the aforementioned element (typically, a tungstensilicide film or a titanium silicide film); or the like can be used.Alternatively, as an alloy containing a plurality of such elements, anAl alloy containing C and Ti, an Al alloy containing Ni, an Al alloycontaining C and Ni, an Al alloy containing C and Mn, or the like can beused. Note that the aforementioned single-element film, a nitride film,an alloy film, a silicide film or the like can have a single-layerstructure or be combined to have a stacked-layer structure. For example,in the case of providing a stacked layer structure, a structure in whichAl is provided between Mo and Ti can be employed. Thus, resistance of Alto heat or chemical reaction can be improved. In the case of silicon, itis preferable to include much impurity (P-type impurities or N-typeimpurities) to improve conductivity.

Next as shown in FIG. 3B, an unnecessary portion of the conductive layer301 is removed by etching so that the conductive layer 301 has apredetermined shape. That is, the conductive layer 301 is processed intothe island shape. In other words, the conductive layer 301 is patterned.As a result, a conductive layer 301A, a conductive layer 301B, aconductive layer 301C, and a conductive layer 301D are formed. Theconductive layer 301A, the conductive layer 301B, the conductive layer301C, and the conductive layer 301D serve as a source electrode, a drainelectrode, a source signal line, or the like.

Next as shown in FIG. 3C, a portion of the semiconductor layer 202A isetched. Thus, an impurity layer in the channel region is removed. As aresult, a transistor 303 is completed. Since the gate electrode 104B isprovided under the semiconductor layer 202A, the transistor 303 is abottom gate transistor, and is also an inversely staggered transistor.In addition, since a channel portion of a semiconductor layer is etched,the transistor 303 is a channel etch transistor.

The semiconductor layer 202A can be formed using an amorphoussemiconductor, a microcrystalline semiconductor, or a semi-amorphoussemiconductor (SAS). Alternatively, a polycrystalline semiconductorlayer may be used. SAS has an intermediate structure between anamorphous and a crystalline structure (including a single-crystal and apolycrystalline), and a third condition that is stable in term of freeenergy. Moreover, SAS includes a crystalline region with a short-rangeorder and lattice distortion. A crystalline region of 0.5 to 20 nm canbe observed at least in part of a film. When silicon is contained as amain component, Raman spectrum shifts to a wave number side lower than520 cm⁻¹. The diffraction peaks of (111) and (220) which are thought tobe derived from the silicon crystalline lattice are observed by X-raydiffraction. SAS contains hydrogen or halogen of at least 1 atomicpercent or more to compensate dangling bonds. SAS is formed by glowdischarge decomposition (plasma CVD) of a material gas. As the materialgas, Si₂H₆, SiH₂Cl₂, SiHCl₃, SiCl₄, SiF₄, or the like as well as SiH₄can be used. Alternatively, GeF₄ may be mixed. The material gas may bediluted with H₂, or H₂ and one or more kinds of rare gas elementsselected from He, Ar, Kr, and Ne. A dilution ratio is in the range of 2to 1000 times. Pressure is in the range of approximately 0.1 to 133 Pa,and a power supply frequency is 1 to 120 MHz, preferably 13 to 60 MHz. Asubstrate heating temperature may be 300° C. or lower. A concentrationof impurities in atmospheric components such as oxygen, nitrogen, andcarbon is preferably 1×10²⁰ cm⁻¹ or less as impurity elements in thefilm. In particular, an oxygen concentration is 5×10¹⁹/cm³ or less,preferably 1×10¹⁹/cm³ or less. Here, an amorphous semiconductor layer isformed using a material containing silicon (Si) as its main component(e.g., Si_(x)Ge_(1-x)) by a sputtering method, an LPCVD method, or aplasma CVD method. Then, the amorphous semiconductor layer iscrystallized by a crystallization method such as a laser crystallizationmethod, a thermal crystallization method using RTA or an annealingfurnace, or a thermal crystallization method using a metal element whichpromotes crystallization.

Next as shown in FIG. 4A, an insulating layer 401 is provided so as tocover the conductive layer 301A, the conductive layer 301B, theconductive layer 301C, and the conductive layer 301D. The insulatinglayer 401 is provided using a CVD method, a sputtering method, a thermaloxidation method, a vapor deposition method, an ink jet method, aprinting method, or the like. The insulating layer 401 also serves as aprotective film. Alternatively, the insulating layer 401 serves as aninsulator of a capacitor element or an interlayer film in some cases.

The insulating layer 401 can be formed by a single-layer structure or astacked-layer structure of a siloxane resin; a film, of silicon oxide(SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride (SiO_(x)N_(y))(x>y), silicon nitride oxide (SiN_(x)O_(y)) (x>y), or the like; a filmcontaining carbon, such as a DLC (diamond-like carbon); an organicmaterial such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; or an insulating film containing oxygen ornitrogen. Note that a siloxane resin corresponds to a resin havingSi—O—Si bonds. Siloxane includes a skeleton structure of a bond ofsilicon (Si) and oxygen (O). As a substituent, an organic groupcontaining at least hydrogen (such as an alkyl group or aromatichydrocarbon) is used. Alternatively, a fluoro group, or a fluoro groupand an organic group containing at least hydrogen can be used as asubstituent.

It is preferable that a portion of the insulating layer 401 in contactwith the semiconductor layer 202, which is provided, be silicon nitride(SiN_(x)). The semiconductor layer 202 includes hydrogen in some cases.In that case, reacting the hydrogen included in the semiconductor layer202 and the insulating layer 401 can be prevented by using siliconnitride (SiN_(x)) as the insulating layer 401.

Note that the insulating layer 401 preferably includes silicon nitride(SiN_(x)). Silicon nitride (SiN_(x)) has a function of blockingimpurities. Therefore, a transistor can be protected from impurities.

Note that the insulating layer 401 preferably includes an organic film.Thus, the surface of the insulating layer 401 can be flattened. When thesurface of the insulating layer 401 is flat, a pixel electrode formedthereover can also be flattened. When a pixel electrode becomes flat, adisplay device can be made appropriately.

Next as shown in FIG. 4B, a contact hole is formed. The contact hole isformed by etching materials using a dry etching method, a wet etching,or the like. Note that when the insulating layer 401 includes theorganic film which is formed of a photosensitive material, the contacthole can be formed at the same time as forming the insulating layer 401.Therefore, the material of the contact hole portion does not need to beetched. Therefore, steps can be reduced. The insulating layer 401A isetched so as to form a contact hole 501A, a contact hole 501B, and acontact hole 501E. The insulating layer 401, the insulating layer 201,and the insulating layer 103 are etched so as to form a contact hole501C and a contact hole 501D.

Next as shown in FIG. 5, a conductive layer 601 is provided so as tocover the insulating layer 401, the contact hole 501A, the contact hole501B, the contact hole 501C, the contact hole 501D, and the contact hole501E. The conductive layer 601 is provided using a CVD method, asputtering method, a thermal oxidation method, a vapor depositionmethod, an ink jet method, a printing method, or the like. Theconductive layer 601 serves as a wiring, a pixel electrode, a lighttransmitting electrode, a reflective electrode, or the like.

The conductive layer 601 can have a single-layer structure of aconductive film or a stacked-layer structure of two or three conductivefilms. Further, the conductive layer 601 preferably includes a regionwhich has high transmittivity of light and is light-transmitting orclose to light-transmitting. Thus, the conductive layer 601 can serve asa pixel electrode of a light transmitting region. In addition, theconductive layer 601 preferably includes a region of high reflectivity.Thus, the conductive layer 601 can serve as a pixel electrode of areflective region.

Note that it is preferable that the conductive layer 601 is a filmincluding ITO, IZO, ZnO, or the like.

Next as shown in FIG. 6, an unnecessary portion of the conductive layer601 is removed by etching so that the conductive layer 601 has apredetermined shape. That is, the conductive layer 601 is processed intothe island shape. In other words, the conductive layer 601 is patterned.

In this case, a patterned conductive layer 601A serves as a pixelelectrode as a patterned conductive layer. However, the presentinvention is not limited this. A conductive layer 601B and a conductivelayer 601C serve as a wiring. The conductive layer 601B has a functionof connecting the conductive layer 301C and the semiconductor layer 102.The conductive layer 601C has a function of connecting the conductivelayer 301D and the semiconductor layer 102.

After that, a display device is completed through various steps inaccordance with the kind of display devices. For example, an orientationfilm is formed, and liquid crystal is provided between a countersubstrate having a color filter and the orientation film. Alternatively,an organic electroluminescence material is provided over the conductivelayer 601A, and a cathode is provided thereover.

Note that, in FIG. 4B, a contact hole is formed, and a conductive layeris provided thereover, so that the conductive layer 301C and thesemiconductor layer 102 are connected. As shown in FIG. 7, conductivelayer 301F and a conductive layer 104C can be connected through acontact hole 501F and a contact hole 501G using a conductive layer 601D.Note that the conductive layer 301F is formed using the conductive layer301, the conductive layer 104C is formed using the conductive layer 104,and the conductive layer 601D is formed using the conductive layer 601.The contact hole 501F and the contact hole 501G are formed at the sametime as forming contact hole 501A, the contact hole 501B, the contacthole 501C, the contact hole 501D, and the like.

Note that in a similar manner to the conductive layer 301C, theconductive layer 301D, and the conductive layer 301F, a semiconductorlayer may be provided under the conductive layers, or a semiconductorlayer is not necessarily provided under the conductive layer 301E asshown in FIG. 7.

Note that, in FIG. 2D, FIG. 3A, FIG. 3B, and FIG. 3C, the semiconductorlayer 202 is patterned using a mask (reticle) which is different fromthat of the conductive layer 301; however, the present invention is notlimited to this. The semiconductor layer 202 and the conductive layer301 can be patterned with one mask (reticle) using a half tone mask, agray tone mask, or the like. FIG. 8 shows a cross sectional view of thatcase. The size of a semiconductor layer 202E is larger than that of theconductive layer 301A and the conductive layer 301B because of using ahalf tone mask, a gray tone mask, or the like. In other words, thesemiconductor layer 202E is necessarily provided under the conductivelayer 301A and the conductive layer 301B.

Note that, in FIG. 6, the conductive layer 301C and the semiconductorlayer 102 are connected through the conductive layer 601B, and theconductive layer 301D and the semiconductor layer 102 are connectedthrough the conductive layer 601C, and in FIG. 7, the conductive layer301F and the conductive layer 104C are connected through the conductivelayer 601D; however, the present invention is not limited to this. Byforming a contact hole, the conductive film and the semiconductor layercan be directly connected without interposing another conductive layer.In other words, as the following step of FIG. 2D or FIG. 2B, theinsulating layer 201 and the insulating layer 103 are etched to form acontact hole, so that the conductive film formed by using the conductivelayer 301 can be directly connect to the conductive film formed by usingthe conductive layer 104 or the semiconductor layer formed by using thesemiconductor layer 102. An example of this case is shown in FIG. 9. InFIG. 9, a conductive layer 301G formed by using the conductive layer 301is directly connected to the semiconductor layer 102 through a contacthole 901A. Similarly, a conductive layer 301H formed by using theconductive layer 301 is directly connected to the semiconductor layer102 through a contact hole 901B. The conductive layer 601E is directlyconnected to the conductive layer 301H through a contact hole 501H. Notethat it is preferable that a semiconductor layer be not provided underthe conductive layer 301H and the conductive layer 301G in the case.This is because when the semiconductor layer 102 is contacted with theconductive layer 301H and the conductive layer 301G, it is preferablethat another layer is not provided therebetween.

Note that, in FIG. 6, the transistor 303 is the channel etch transistor;however, the present invention is not limited to this. A channelprotective transistor can also be used. An example of this case is shownin FIG. 10. In the channel protective transistor, semiconductor layersare not provided successively, but an insulating layer 1001 forprotecting a channel from etching is provided therebetween. In otherwords, the insulating layer 1001 is provided over a semiconductor layer1002 which is intrinsic, and a semiconductor layer 1003A and asemiconductor layer 1003B are provided thereover. The semiconductorlayer 1003A and the semiconductor layer 1003B include an impurity(N-type or P-type).

Note that, in FIG. 10, the semiconductor layer 1002 is patterned, andthen, the semiconductor layer 1003A, the semiconductor layer 1003B, theconductive layer 301A, and the conductive layer 301B are patternedconcurrently; however, the present invention is not limited to this. Thesemiconductor layer 1002, the semiconductor layer 1003A, thesemiconductor layer 1003B, the conductive layer 301A, and the conductivelayer 301B can be patterned concurrently. In that case, thesemiconductor layer 1002 is necessarily provided under the conductivelayer 301A and the conductive layer 301B.

The structures and manufacturing methods of transistors have beendescribed above. Note that a wiring, an electrode, a conductive layer, aconductive film, a terminal, a via, a plug, or the like is preferablyformed of one element or a plurality of elements of a group consistingof aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum (Mo),tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni), platinum (Pt),gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium (Sc),cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si), phosphorus (P),boron (B), arsenic (As), gallium (Ga), indium (In), tin (Sn), and oxygen(O), or a compound or an alloy material including one element or aplurality of such elements (e.g., indium tin oxide (ITO), indium zincoxide (IZO), indium tin oxide to which silicon oxide is added (ITSO),zinc oxide (ZnO), tin oxide (SnO), cadmium tin oxide (CTO), aluminumneodymium (Al—Nd), magnesium silver (Mg—Ag), or molybdenum neodymium(Mo—Nb)). Alternatively, a wiring, an electrode, a conductive layer, aconductive film, a terminal, or the like is preferably formed of asubstance or the like obtained by combining such compounds.Alternatively, such a wiring, an electrode, a conductive layer, aconductive film, a terminal are preferably formed to have a substanceincluding a compound of silicon and one or more of the elements selectedfrom the above group (silicide) (e.g., aluminum silicon, molybdenumsilicon, nickel silicide); or a compound of nitrogen and one or more ofthe elements selected from the group (e.g., titanium nitride, tantalumnitride, or molybdenum nitride).

Note that silicon (Si) may include an n-type impurity (such asphosphorus) or a p-type impurity (such as boron). When silicon includessuch impurity, conductivity is improved, so that the silicon can behavein a similar manner to a normal conductor. Thus, such silicon can beutilized easily as wirings or electrodes.

Silicon can be various types of silicon such as single-crystallinesilicon, polycrystalline silicon, or microcrystalline silicon.Alternatively, silicon having no crystallinity such as amorphous siliconcan be used. By using single-crystalline silicon or polycrystallinesilicon, resistance of a wiring, an electrode, a conductive layer, aconductive film, a terminal, or the like can be reduced. By usingamorphous silicon or microcrystalline silicon, a wiring or the like canbe formed by a simple process.

Note that aluminum or silver has high conductivity, and thus can reducea signal delay. Since aluminum or silver can be easily etched, aluminumor silver can be easily patterned and processed minutely.

Note that copper has high conductivity; therefore, signal delay can bedecreased by using copper. In using copper, a stacked structure ispreferably employed to enhance adhesiveness.

Molybdenum or titanium is preferable since molybdenum or titanium doesnot cause defects even if molybdenum or titanium is in contact with anoxide semiconductor (e.g., ITO or IZO) or silicon. Further, molybdenumor titanium is easily etched and has high heat resistance.

Tungsten is preferable since it has an advantage such as high heatresistance.

Neodymium is preferable because it has an advantage such as high heatresistance. In particular, when an alloy of neodymium and aluminum isused, heat resistance is improved, and thus, hillocks of aluminum arenot easily generated.

Silicon is preferable since it can be formed at the same time as asemiconductor layer included in a transistor and has high heatresistance.

Note that ITO, IZO, ITSO, zinc oxide (ZnO), silicon (Si), tin oxide(SnO), or cadmium tin oxide (CTO) can be used for a portion whichtransmits light because it has a light-transmitting property. Forexample, it can be used for a pixel electrode or a common electrode.

IZO is preferable since it is easily etched and processed. In etchingIZO, residues of IZO are hardly left. Thus, when a pixel electrode isformed using IZO, defects (such as short-circuiting or orientationdisorder) of a liquid crystal element or a light-emitting element can bereduced.

A wiring, an electrode, a conductive layer, a conductive film, aterminal, a via, a plug, or the like may have a single-layer structureor a multi-layer structure. By employing a single-layer structure, amanufacturing process of such a wiring, an electrode, a conductivelayer, a conductive film, or a terminal can be simplified; the number ofdays for a process can be reduced; and cost can be reduced.Alternatively, by employing a multilayer structure, an advantage of eachmaterial is utilized and a disadvantage thereof is reduced so that awiring, an electrode, or the like with high performance can be formed.For example, a low-resistant material (e.g., aluminum) is included in amultilayer structure, thereby reducing the resistance of such wirings.As another example, when a low heat-resistant material is interposedbetween high heat-resistant materials to form a stacked-layer structure,heat resistance of wirings or electrodes can be increased, utilizingadvantages of a low heat-resistance material. For example, a layerincluding aluminum is preferably interposed between layers includingmolybdenum, titanium, neodymium, or the like as a stacked-layerstructure.

If wirings or electrodes are in direct contact with each other, anadverse effect is caused to each other in some cases. For example, amaterial of a wiring, an electrode, or the like is mixed into a materialof the other wiring, electrode, or the like, and properties of thematerials are changed, so that the original object cannot be achieved.As another example, when a high-resistant portion is formed, a problemmay occur, so that the high-resistant portion cannot be normally formed.In such cases, a reactive material is preferably interposed by orcovered with a material which does not react easily to form astacked-layer structure. For example, when ITO is connected to aluminum,titanium, molybdenum, or an alloy of neodymium is preferably disposedbetween the ITO and the aluminum. As another example, when silicon isconnected to aluminum, titanium, molybdenum, or an alloy of neodymium ispreferably disposed between the silicon and the aluminum.

Note that the term “wiring” indicates a portion including a conductor.The wiring may be extended in a long linear shape or may be short.Therefore, electrodes are included in such wirings.

Note that a carbon nanotube may be used for a wiring, an electrode, aconductive layer, a terminal, a via, a plug, or the like. Since a carbonnanotube has a light-transmitting property, it can be used for a portionwhich transmits light. For example, it can be used for a pixel electrodeor a common electrode.

A cross-sectional view has been shown. Next, an example of a layoutpattern is shown. FIG. 11 is a layout pattern in which two transistors203 are provided. A gate electrode 104AA is provided over asemiconductor layer 102AA and a semiconductor layer 102BB so as to formthe transistor. A first power supply line 301AA is connected to thesemiconductor layer 102AA through a contact hole using a conductivelayer 601AA. Similarly, a second power supply line 301CC is connected tothe semiconductor layer 102BB through a contact hole using a conductivelayer 601CC. An output wiring 301BB is connected to the semiconductorlayer 102AA and the semiconductor layer 102BB through a contact hole501AA and a contact hole 501BB using a conductive layer 601BB.

Note that a circuit shown in FIG. 11 can operate as an inverter circuitor a source follower circuit.

In this manner, a circuit configured by the transistor 203 has highmobility and high current supply capacity; thus, it is preferable to beused as a driver circuit. On the other hand, since mobility of thetransistor 303 is not high and the transistor 303 can be manufactured ina large size, it is preferable to be used as a pixel circuit.

Although this embodiment mode is described with reference to variousdrawings, the contents (or may be part of the contents) described ineach drawing can be freely applied to, combined with, or replaced withthe contents (or may be part of the contents) described in anotherdrawing. Further, much more drawings can be formed by combining eachpart in the above-described drawings with another part.

Similarly, the contents (or a part thereof) described in each drawing ofthis embodiment mode can be freely applied to, combined with, orreplaced with the contents (or a part thereof) described in a drawing inanother embodiment mode. Further, much more drawings can be formed bycombining each part in the drawings in this embodiment mode with part ofanother embodiment mode.

Note that this embodiment mode has described just examples of embodying,slightly transforming, modifying, improving, describing in detail, orapplying the contents (or part of the contents) described in otherembodiment modes, an example of related part thereof, or the like.Therefore, the contents described in other embodiment modes can befreely applied to, combined with, or replaced with this embodiment mode.

Embodiment Mode 2

Next, an arranging method of the semiconductor layer used for thesingle-crystal TFT is described.

FIGS. 12A and 12B show an SOI substrate of the present invention. InFIG. 12A, a base substrate 9200 is a substrate having an insulatingsurface or an insulating substrate, and a variety of glass substratesthat are used in the electronics industry, such as aluminosilicateglass, aluminoborosilicate glass, or barium borosilicate glass, can beused. Alternatively, a quartz glass substrate or a semiconductorsubstrate such as a silicon wafer can be used. An SOI layer 9202 is asingle-crystal semiconductor, and single-crystal silicon is typicallyapplied thereto. Alternatively, a semiconductor layer which is separatedfrom a single-crystal semiconductor layer or a polycrystal semiconductorlayer of silicon or germanium using a hydrogen ion implantationseparation method can be applied. Alternatively, crystallinesemiconductor layer formed by using a compound semiconductor such asgallium arsenide or indium phosphide can be applied.

Between the base substrate 9200 and the SOI layer 9202 described above,a bonding layer 9204 which has a smooth surface and forms a hydrophilicsurface is provided. A silicon oxide film is suitable for the bondinglayer 9204. In particular, a silicon oxide film formed by a chemicalvapor deposition method using an organic silane gas is preferable. As anorganic silane gas, a silicon-containing compound such astetraethoxysilane (TEOS) (chemical formula: Si(OC₂H₅)₄),tetramethylsilane (TMS), tetramethylcyclotetrasiloxane (TMCTS),octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane (HMDS),triethoxysilane (chemical formula: SiH(OC₂H₅)₃), ortrisdimethylaminosilane (chemical formula: SiH(N(CH₃)₂)₃) can be used.

The bonding layer 9204 which has a smooth surface and forms ahydrophilic surface is provided with a thickness of 5 to 500 nm. Withsuch a thickness, roughness of a surface on which the bonding layer 9204is formed can be smoothed and smoothness of a growth surface of the filmcan be ensured. In addition, distortion between the base substrate 9200and the SOI layer 9202 which are bonded to each other can be reduced.The base substrate 9200 may be provided with a similar silicon oxidefilm. That is, when the SOI layer 9202 is bonded to the base substrate9200 which is a substrate having an insulating surface or an insulatingsubstrate, the base substrate 9200 and the SOI layer 9202 can be firmlybonded to each other when the bonding layer 9204 formed of a siliconoxide film which is preferably formed using organic silane as a materialis provided on either one or both surfaces of the base substrate 9200and the SOI layer 9202 which are to be bonded.

FIG. 12B shows a structure in which the base substrate 9200 is providedwith a barrier layer 9205 and the bonding layer 9204. In the case ofbonding the SOI layer 9202 to the base substrate 9200, the SOI layer9202 can be prevented from being contaminated by diffusion of impuritiessuch as mobile ions like alkali metal or alkaline earth metal from aglass substrate which is used as the base substrate 9200. A bondinglayer 9204 on the base substrate 9200 side may be provided asappropriate.

FIG. 13A shows a structure in which a nitrogen-containing insulatinglayer 9220 is provided between the SOI layer 9202 and the bonding layer9204. The nitrogen-containing insulating layer 9220 is formed bystacking one or a plurality of films selected from a silicon nitridefilm, a silicon nitride oxide film, and a silicon oxynitride film. Forexample, the nitrogen-containing insulating layer 9220 can be formed bystacking a silicon oxynitride film and a silicon nitride oxide film fromthe SOI layer 9202 side. The bonding layer 9204 is provided in order toform a bond with the base substrate 9200, whereas thenitrogen-containing insulating layer 9220 is preferably provided inorder to prevent the SOI layer 9202 from being contaminated by diffusionof impurities such as mobile ions or moisture.

Note that here, a silicon oxynitride film corresponds to a film whichcontains more oxygen than nitrogen, and for example, includes oxygen,nitrogen, silicon, and hydrogen at concentrations ranging from 50 to 70at. %, 0.5 to 15 at. %, 25 to 35 at. %, and 0.1 to 10 at. %,respectively. In addition, a silicon nitride oxide film corresponds to afilm which contains more nitrogen than oxygen and includes oxygen,nitrogen, silicon, and hydrogen at concentrations ranging from 5 to 30at. %, 20 to 55 at. %, 25 to 35 at. %, and 10 to 25 at. %, respectively.Note that the above range is a measurement result using Rutherfordbackscattering spectrometry (RBS) and hydrogen forward scattering (HFS).Note that the content percentages of the component atoms is not beyond100 at. %

FIG. 13B shows a structure in which the base substrate 9200 is providedwith the bonding layer 9204. Between the base substrate 9200 and thebonding layer 9204, the barrier layer 9205 is preferably provided. Thebarrier layer 9205 is provided in order to prevent the SOI layer 9202from being contaminated by diffusion of impurities such as mobile ionslike alkali metal or alkaline earth metal from a glass substrate whichis used as the base substrate 9200. In addition, the SOI layer 9202 isprovided with a silicon oxide film 9221. The silicon oxide film 9221forms a bond with the bonding layer 9204 to fix the SOI layer 9202 overthe base substrate 9200. The silicon oxide film 9221 is preferablyformed by thermal oxidation. Alternatively, similarly to the bondinglayer 9204, the silicon oxide film 9221 may be formed by a chemicalvapor deposition method using TEOS. Further alternatively, as thesilicon oxide film 9221, chemical oxide can be used. Chemical oxide canbe formed by, for example, performing treatment on a surface of asemiconductor substrate by using ozone-containing water. Chemical oxideis preferable because it reflects flatness of the surface of thesemiconductor substrate.

A method for manufacturing such an SOI substrate is described withreference to FIGS. 14A to 15.

A semiconductor substrate 9201 shown in FIG. 14A is cleaned, and ionswhich are accelerated by an electric field are injected into reach apredetermined depth from the surface of the semiconductor substrate 9201to form a fragile layer 9203. Irradiation or injection of ions isconducted in consideration of the thickness of an SOI layer which is tobe formed over a base substrate. The thickness of the SOI layer is 5 to500 nm, preferably 10 to 200 nm. Accelerating voltage for injecting ionsinto the semiconductor substrate 9201 is set in consideration of such athickness. The fragile layer 9203 is formed by injecting ions ofhydrogen, helium, or halogen typified by fluorine. In this case, it ispreferable to use one ion or plural ions formed of the same atoms whichhave different mass. In the case of irradiating hydrogen ions, thehydrogen ions preferably include H⁺, H₂ ⁺, and H₃ ⁺ ions with a highpercentage of H₃ ⁺ ions. With a high percentage of H₃ ⁺ ions,irradiation efficiency can be increased and irradiating time can beshortened. With such a structure, separation can be easily performed.

In the case of irradiation with ions at a high dose, the surface of thesemiconductor substrate 9201 is roughened in some cases. Therefore, aprotective film against irradiation with ions, such as a silicon nitridefilm, a silicon nitride oxide film, or the like with a thickness of 50to 200 nm may be provided on a surface with which ions are irradiated.

Next, as shown in FIG. 14B, a silicon oxide film is formed over asurface to which the base substrate is bonded as a bonding layer 9204.As the silicon oxide film, a silicon oxide film formed by a chemicalvapor deposition method using an organic silane gas as described aboveis preferably used. Alternatively, a silicon oxide film formed by achemical vapor deposition method using a silane gas can be used. In filmformation by a chemical vapor deposition method, film formationtemperature at, for example, 350° C. or lower, at which degassing of thefragile layer 9203 formed in a single-crystal semiconductor substratedoes not occur, is used. Heat treatment for separating an SOI layer froma single-crystal or polycrystalline semiconductor substrate is performedat a higher temperature than the film formation temperature.

FIG. 14C shows a mode in which a surface of the base substrate 9200 anda surface of the semiconductor substrate 9201, on which the bondinglayer 9204 is formed are disposed in contact to be bonded to each other.The surfaces which are to be bonded are cleaned sufficiently. Then, whenthe base substrate 9200 and the bonding layer 9204 are disposed incontact, a bond is formed. This bond is formed by Van der Waals forces.When the base substrate 9200 and the semiconductor substrate 9201 arepressed against each other, a stronger bond can be formed by hydrogenbonding.

In order to form a favorable bond, the surfaces may be activated. Forexample, the surfaces which are to form a bond are irradiated with anatomic beam or an ion beam. When an atomic beam or an ion beam is used,an inert gas neutral atom beam or inert gas ion beam of argon or thelike can be used. Alternatively, plasma irradiation or radical treatmentis performed. With such a surface treatment, a bond between differentkinds of materials can be easily formed even at a temperature of 200 to400° C.

After the base substrate 9200 and the semiconductor substrate 9201 arebonded to each other with the bonding layer 9204 interposedtherebetween, heat treatment or pressure treatment is preferablyperformed. When heat treatment or pressure treatment is performed,bonding strength can be increased. Temperature of heat treatment ispreferably lower than or equal to the upper temperature limit of thebase substrate 9200. Pressure treatment is performed so that pressure isapplied in a perpendicular direction to the bonded surface, inconsideration of pressure resistance of the base substrate 9200 and thesemiconductor substrate 9201.

In FIG. 15, after the base substrate 9200 and the semiconductorsubstrate 9201 are bonded to each other, heat treatment is performed toseparate the semiconductor substrate 9201 at the fragile layer 9203. Theheat treatment is preferably performed at a temperature higher than orequal to the film formation temperature of the bonding layer 9204 andlower than or equal to the upper temperature limit of the base substrate9200. When the heat treatment is performed at, for example, 400 to 600°C., the volume of fine voids formed in the fragile layer 9203 ischanged, so that separation (cleavage) can be performed along thefragile layer 9203. Since the bonding layer 9204 is bonded to the basesubstrate 9200, the SOI layer 9202 having the same crystallinity as thesemiconductor substrate 9201 remains over the base substrate 9200.

FIG. 16A to 16C show steps of forming an SOI layer with a bonding layerprovided on the base substrate 9200 side. FIG. 16A shows a step in whichions which are accelerated by an electric field are injected into thesemiconductor substrate 9201 which is provided with the silicon oxidefilm 9221 at a predetermined depth to form the fragile layer 9203.Injecting of ions of hydrogen, helium, or a halogen typified by fluorineis performed similarly to the case shown in FIG. 14A. When the siliconoxide film 9221 is formed on the surface of the semiconductor substrate9201, the surface of the semiconductor substrate 9201 can be preventedfrom being damaged by ion irradiation and from losing its flatness.

FIG. 16B shows a step in which a surface of the base substrate 9200provided with the barrier layer 9205 and the bonding layer 9204 and thesurface of the semiconductor substrate 9201, on which the silicon oxidefilm 9221 is formed are disposed in contact to be bonded. A bond isformed when the bonding layer 9204 over the base substrate 9200 isdisposed in close contact with the silicon oxide film 9221 formed on thesemiconductor substrate 9201.

After that, as shown in FIG. 16C, the semiconductor substrate 9201 isseparated. Heat treatment for separating the semiconductor substrate9201 is performed similarly to the case shown in FIG. 15. In thismanner, the SOI substrate shown in FIG. 13B can be obtained.

In this manner, in accordance with this mode, even if a substrate withan upper temperature limit of 700° C. or lower, such as a glasssubstrate or the like, is used as the base substrate 9200, the SOI layer9202 having strong adhesiveness of a bonded portion can be obtained. Asthe base substrate 9200, various glass substrates which are used in theelectronics industry and are referred to as non-alkali glass substrates,such as aluminosilicate glass substrates, aluminoborosilicate glasssubstrates, and barium borosilicate glass substrates can be used. Thatis, a single-crystal semiconductor layer can be formed over a substratewhich is longer than one meter on a side. When such a large-areasubstrate is used, not only a display device such as a liquid crystaldisplay but also a semiconductor integrated circuit can be manufactured.

Note that a manufacturing method and an arrangement method of thesemiconductor layer are not limited to this. An amorphous silicon filmcan be formed over an insulating substrate by a CVD method, or the like,and amorphous silicon film is crystallized by irradiated with laser(linear laser, continuous solid oscillation laser, or the like) or byapplying heat or the like, so that polycrystalline silicon ormicrocrystalline silicon can be manufactured.

Although this embodiment mode is described with reference to variousdrawings, the contents (or may be part of the contents) described ineach drawing can be freely applied to, combined with, or replaced withthe contents (or may be part of the contents) described in anotherdrawing. Further, much more drawings can be formed by combining eachpart in the above-described drawings with another part.

Similarly, the contents (or may be part of the contents) described ineach drawing of this embodiment mode can be freely applied to, combinedwith, or replaced with the contents (or may be part of the contents)described in a drawing in another embodiment mode. Further, much moredrawings can be formed by combining each part in the drawings in thisembodiment mode with part of another embodiment mode. Note that thisembodiment mode has described just examples of embodying, slightlytransforming, modifying, improving, describing in detail, or applyingthe contents (or part of the contents) described in other embodimentmodes, an example of related part thereof, or the like. Therefore, thecontents described in other embodiment modes can be freely applied to,combined with, or replaced with this embodiment mode.

Embodiment Mode 3

In this embodiment mode, a peripheral portion of a liquid crystal panelis described.

FIG. 17 shows an example of a liquid crystal display device including aso-called edge-light type backlight unit 5201 and a liquid crystal panel5207. An edge-light type corresponds to a type in which a light sourceis provided at an end of a backlight unit and fluorescence of the lightsource is emitted from the entire light-emitting surface. The edge-lighttype backlight unit is thin and can save power.

The backlight unit 5201 includes a diffusion plate 5202, a light guideplate 5203, a reflection plate 5204, a lamp reflector 5205, and a lightsource 5206.

The light source 5206 has a function of emitting light as necessary. Forexample, as the light source 5206, a cold cathode fluorescent lamp, ahot cathode fluorescent lamp, a light-emitting diode, an inorganic ELelement, an organic EL element, or the like is used.

FIGS. 18A to 18D are views each showing a detailed structure of theedge-light type backlight unit. Note that description of a diffusionplate, a light guide plate, a reflection plate, and the like is omitted.

A backlight unit 5211 shown in FIG. 18A has a structure in which a coldcathode fluorescent lamp 5213 is used as a light source. In addition, alamp reflector 5212 is provided to efficiently reflect light from thecold cathode fluorescent lamp 5213. Such a structure is often used for alarge display device because luminance of light obtained from the coldcathode fluorescent lamp is high.

A backlight unit 5221 shown in FIG. 18B has a structure in whichlight-emitting diodes (LEDs) 5223 are used as light sources. Forexample, the light-emitting diodes (LEDs) 5223 which emit white lightare provided at a predetermined interval. In addition, a lamp reflector5222 is provided to efficiently reflect light from the light-emittingdiodes (LEDs) 5223.

A backlight unit 5231 shown in FIG. 18C has a structure in whichlight-emitting diodes (LEDs) 5233, light-emitting diodes (LEDs) 5234,and light-emitting diodes (LEDs) 5235 of R, G, and B are used as lightsources. The light-emitting diodes (LEDs) 5233, the light-emittingdiodes (LEDs) 5234, and the light-emitting diodes (LEDs) 5235 of R, G,and B are each provided at a predetermined interval. By using thelight-emitting diodes (LEDs) 5233, the light-emitting diodes (LEDs)5234, and the light-emitting diodes (LEDs) 5235 of R, G, and B, colorreproductivity can be improved. In addition, a lamp reflector 5232 isprovided to efficiently reflect light from the light-emitting diodes.

A backlight unit 5241 shown in FIG. 18D has a structure in whichlight-emitting diodes (LEDs) 5243, light-emitting diodes (LEDs) 5244,and light-emitting diodes (LEDs) 5245 of R, G, and B are used as lightsources. For example, among the light-emitting diodes (LEDs) 5243, thelight-emitting diodes (LEDs) 5244, and the light-emitting diodes (LEDs)5245 of R, G, and B, a plurality of the light-emitting diodes of a colorwith low emission intensity (e.g., green) are provided. By using thelight-emitting diodes (LEDs) 5243, the light-emitting diodes (LEDs)5244, and the light-emitting diodes (LEDs) 5245 of R, G, and B, colorreproductivity can be improved. In addition, a lamp reflector 5242 isprovided to efficiently reflect light from the light-emitting diodes.

FIG. 21 shows an example of a liquid crystal display device including aso-called direct-type backlight unit and a liquid crystal panel. Adirect type corresponds to a type in which a light source is provideddirectly under a light-emitting surface and fluorescence of the lightsource is emitted from the entire light-emitting surface. Thedirect-type backlight unit can efficiently utilize the amount of emittedlight.

A backlight unit 5290 includes a diffusion plate 5291, a light-shieldingplate 5292, a lamp reflector 5293, a light source 5294, and a liquidcrystal panel 5295.

The light source 5294 has a function of emitting light as necessary. Forexample, as the light source 5294, a cold cathode fluorescent lamp, ahot cathode fluorescent lamp, a light-emitting diode, an inorganic ELelement, an organic EL element, or the like is used.

FIG. 19 shows an example of a structure of a polarizing plate (alsoreferred to as a polarizing film).

A polarizing film 5250 includes a protective film 5251, a substrate film5252, a PVA polarizing film 5253, a substrate film 5254, an adhesivelayer 5255, and a mold release film 5256.

When the PVA polarizing film 5253 is sandwiched by films to be basematerials (the substrate film 5252 and the substrate film 5254) fromboth sides, reliability can be improved. Note that the PVA polarizingfilm 5253 may be sandwiched by triacetylcellulose (TAC) films with highlight-transmitting properties and high durability. Note that each of thesubstrate films and the TAC films function as protective films ofpolarizer included in the PVA polarizing film 5253.

One of the substrate films (the substrate film 5254) is provided withthe adhesive layer 5255 which is to be attached to a glass substrate ofthe liquid crystal panel. Note that the adhesive layer 5255 is formed byapplying an adhesive to one of the substrate films (the substrate film5254). The mold release film 5256 (a separate film) is provided to theadhesive layer 5255.

The protective film 5251 is provided to the other of the substratesfilms (the substrate film 5252).

A hard coating scattering layer (an anti-glare layer) may be provided ona surface of the polarizing film 5250. Since the surface of the hardcoating scattering layer has minute unevenness formed by AG treatmentand has an anti-glare function which scatters external light, reflectionof external light in the liquid crystal panel can be prevented. Surfacereflection can also be prevented.

Note that a treatment in which plurality of optical thin film layershaving different refractive indexes are layered (also referred to asanti-reflection treatment or AR treatment) may be performed on thesurface of the polarizing film 5250. The plurality of layered opticalthin film layers having different refractive indexes can reducereflectivity on the surface by an interference effect of light.

FIGS. 20A to 20C each show an example of a system block of the liquidcrystal display device.

In a pixel portion 5265, signal lines 5269 which are extended from asignal line driver circuit 5263 are provided. In addition, in the pixelportion 5265, scan lines 5260 which are extended from a scan line drivercircuit 5264 are also provided. In addition, a plurality of pixels arearranged in matrix in cross regions of the signal lines 5269 and thescan lines 5260. Note that each of the plurality of pixels includes aswitching element. Therefore, voltage for controlling inclination ofliquid crystal molecules can be separately input to each of theplurality of pixels. A structure in which a switching element isprovided in each cross region in this manner is referred to as an activematrix type. Note that the present invention is not limited to such anactive matrix type and a structure of a passive matrix type may be used.Since the passive matrix type does not have a switching element in eachpixel, a process is simple.

A driver circuit portion 5268 includes a control circuit 5262, thesignal line driver circuit 5263, and the scan line driver circuit 5264.An image signal 5261 is input to the control circuit 5262. The signalline driver circuit 5263 and the scan line driver circuit 5264 arecontrolled by the control circuit 5262 in accordance with this imagesignal 5261. Therefore, the control circuit 5262 inputs a control signalto each of the signal line driver circuit 5263 and the scan line drivercircuit 5264. Then, in accordance with this control signal, the signalline driver circuit 5263 inputs a video signal to each of the signallines 5269 and the scan line driver circuit 5264 inputs a scan signal toeach of the scan lines 5260. Then, the switching element included in thepixel is selected in accordance with the scan signal and the videosignal is input to a pixel electrode of the pixel.

Note that the control circuit 5262 also controls a power source 5267 inaccordance with the image signal 5261. The power source 5267 includes aunit for supplying power to a lighting unit 5266. As the lighting unit5266, an edge-light type backlight unit or a direct-type backlight unitcan be used. Note that a front light may be used as the lighting unit5266. A front light corresponds to a plate-like lighting unit includinga luminous body and a light conducting body, which is attached to thefront surface side of a pixel portion and illuminates the whole area. Byusing such a lighting unit, the pixel portion can be uniformlyilluminated at low power consumption.

As shown in FIG. 20B, the scan line driver circuit 5264 includes a shiftregister 5271, a level shifter 5272, and a circuit functioning as abuffer 5273. A signal such as a gate start pulse (GSP) or a gate clocksignal (GCK) is input to the shift register 5271.

As shown in FIG. 20C, the signal line driver circuit 5263 includes ashift register 5281, a first latch 5282, a second latch 5283, a levelshifter 5284, and a circuit functioning as a buffer 5285. The circuitfunctioning as the buffer 5285 corresponds to a circuit which has afunction of amplifying a weak signal and includes an operationalamplifier or the like. A signal such as a source start pulse (SSP) orthe like is input to the level shifter 5284 and data (DATA) such as avideo signal is input to the first latch 5282. A latch (LAT) signal canbe temporally held in the second latch 5283 and are simultaneously inputto the pixel portion 5265. This is referred to as line sequentialdriving. Therefore, when a pixel is used in which not line sequentialdriving but dot sequential driving is performed, the second latch can beomitted.

Note that in this embodiment mode, various liquid crystal panels can beused for the liquid crystal panel. For example, a structure in which aliquid crystal layer is sealed between two substrates can be used as theliquid crystal panel. A transistor, a capacitor, a pixel electrode, analignment film, or the like is formed over one of the substrates. Apolarizing plate, a retardation plate, or a prism sheet may be providedon the surface opposite to a top surface of the one of the substrates. Acolor filter, a black matrix, a counter electrode, an alignment film, orthe like is provided on the other of the substrates. A polarizing plateor a retardation plate may be provided on the surface opposite to a topsurface of the other of the substrates. The color filter and the blackmatrix may be formed over the top surface of the one of the substrates.Note that three-dimensional display can be performed by providing a slit(a grid) on the top surface side of the one of the substrates or thesurface opposite to the top surface side of the one of the substrates.

Each of the polarizing plate, the retardation plate, and the prism sheetcan be provided between the two substrates. Alternatively, each of thepolarizing plate, the retardation plate, and the prism sheet can beintegrated with one of the two substrates.

Note that although this embodiment mode is described with reference tovarious drawings, the contents (or may be part of the contents)described in each drawing can be freely applied to, combined with, orreplaced with the contents (or may be part of the contents) described inanother drawing. Further, even more drawings can be formed by combiningeach part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described ineach drawing of this embodiment mode can be freely applied to, combinedwith, or replaced with the contents (or may be part of the contents)described in a drawing in another embodiment mode. Further, even moredrawings can be formed by combining each part with part of anotherembodiment mode in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of thecontents (or may be part of the contents) described in other embodimentmodes, an example of slight transformation thereof, an example ofpartial modification thereof, an example of improvement thereof, anexample of detailed description thereof, an application example thereof,an example of related part thereof, or the like. Therefore, the contentsdescribed in other embodiment modes can be freely applied to, combinedwith, or replaced with this embodiment mode.

Embodiment Mode 4

In this embodiment mode, a pixel structure and an operation of a pixelwhich can be applied to a liquid crystal display device are described.

In this embodiment mode, as an operation mode of a liquid crystalelement, a TN (twisted nematic) mode, an IPS (in-plane-switching) mode,an FFS (fringe field switching) mode, an MVA (multi-domain verticalalignment) mode, a PVA (patterned vertical alignment) mode, an ASM(axially symmetric aligned micro-cell) mode, an OCB (optical compensatedbirefringence) mode, an FLC (ferroelectric liquid crystal) mode, an AFLC(antiferroelectric liquid crystal) mode, or the like can be used.

FIG. 22A shows an example of a pixel structure which can be applied tothe liquid crystal display device.

A pixel 5600 includes a transistor 5601, a liquid crystal element 5602,and a capacitor 5603. A gate of the transistor 5601 is connected to awiring 5605. A first terminal of the transistor 5601 is connected to awiring 5604. A second electrode of the transistor 5601 is connected to afirst electrode of the liquid crystal element 5602 and a first electrodeof the capacitor 5603. A second electrode of the liquid crystal element5602 corresponds to a counter electrode 5607. A second electrode of thecapacitor 5603 is connected to a wiring 5606.

The wiring 5604 functions as a signal line. The wiring 5605 functions asa scan line. The wiring 5606 functions as a capacitor line. Thetransistor 5601 functions as a switch. The capacitor 5603 functions as astorage capacitor.

It is acceptable as long as the transistor 5601 functions as a switch,and the transistor 5601 may be either a P-channel transistor or anN-channel transistor.

FIG. 22B shows an example of a pixel structure which can be applied tothe liquid crystal display device. In particular, FIG. 22B shows anexample of a pixel structure which can be applied to a liquid crystaldisplay device suitable for a horizontal electric field mode (includingan IPS mode and an FFS mode).

A pixel 5610 includes a transistor 5611, a liquid crystal element 5612,and a capacitor 5613. A gate of the transistor 5611 is connected to awiring 5615. A first terminal of the transistor 5611 is connected to awiring 5614. A second terminal of the transistor 5611 is connected to afirst electrode of the liquid crystal element 5612 and a first electrodeof the capacitor 5613. A second electrode of the liquid crystal element5612 is connected to a wiring 5616. A second electrode of the capacitor5613 is connected to the wiring 5616.

The wiring 5614 functions as a signal line. The wiring 5615 functions asa scan line. The wiring 5616 functions as a capacitor line. Thetransistor 5611 functions as a switch. The capacitor 5613 functions as astorage capacitor.

It is acceptable as long as the transistor 5611 functions as a switch,and the transistor 5611 may be a P-channel transistor or an N-channeltransistor.

FIG. 23 shows an example of a pixel structure which can be applied tothe liquid crystal display device. In particular, FIG. 23 shows anexample of a pixel structure in which an aperture ratio of a pixel canbe increased by reducing the number of wirings.

FIG. 23 shows two pixels which are provided in the same column direction(a pixel 5620 and a pixel 5630). For example, when the pixel 5620 isprovided in an N-th row, the pixel 5630 is provided in an (N+1)th row.

A pixel 5620 includes a transistor 5621, a liquid crystal element 5622,and a capacitor 5623. A gate of the transistor 5621 is connected to awiring 5625. A first terminal of the transistor 5621 is connected to awiring 5624. A second terminal of the transistor 5621 is connected to afirst electrode of the liquid crystal element 5622 and a first electrodeof the capacitor 5623. A second electrode of the liquid crystal element5622 corresponds to a counter electrode 5627. A second electrode of thecapacitor 5623 is connected to a wiring which is the same as a wiringconnected to a gate of a transistor of the previous row.

A pixel 5630 includes a transistor 5631, a liquid crystal element 5632,and a capacitor 5633. A gate of the transistor 5631 is connected to awiring 5635. A first terminal of the transistor 5631 is connected to thewiring 5624. A second terminal of the transistor 5631 is connected to afirst electrode of the liquid crystal element 5632 and a first electrodeof the capacitor 5633. A second electrode of the liquid crystal element5632 corresponds to a counter electrode 5637. A second electrode of thecapacitor 5633 is connected to the wiring which is the same as thewiring connected to the gate of the transistor of the previous row (thewiring 5625).

The wiring 5624 functions as a signal line. The wiring 5625 functions asa scan line of the N-th row. The wiring 5625 also functions as a scanline of the (N+1)th row. The transistor 5621 functions as a switch. Thecapacitor 5623 functions as a storage capacitor.

The wiring 5635 functions as a scan line of the (N+1)th row. The wiring5635 also functions as a scan line of the (N+2)th row. The transistor5631 functions as a switch. The capacitor 5633 functions as a storagecapacitor.

It is acceptable as long as each of the transistor 5621 and thetransistor 5631 functions as a switch, and each of the transistor 5621and the transistor 5631 may be either a P-channel transistor or anN-channel transistor.

FIG. 24 shows an example of a pixel structure which can be applied tothe liquid crystal display device. In particular, FIG. 24 shows anexample of a pixel structure in which a viewing angle can be improved byusing a subpixel.

A pixel 5659 includes a subpixel 5640 and a subpixel 5650. Although thecase in which the pixel 5659 includes two subpixels is described, thepixel 5659 may include three or more subpixels.

The subpixel 5640 includes a transistor 5641, a liquid crystal element5642, and a capacitor 5643. A gate of the transistor 5641 is connectedto a wiring 5645. A first terminal of the transistor 5641 is connectedto a wiring 5644. A second terminal of the transistor 5641 is connectedto a first electrode of the liquid crystal element 5642 and a firstelectrode of the capacitor 5643. A second electrode of the liquidcrystal element 5642 corresponds to a counter electrode 5647. A secondelectrode of the capacitor 5643 is connected to a wiring 5646.

The subpixel 5650 includes a transistor 5651, a liquid crystal element5652, and a capacitor 5653. A gate of the transistor 5651 is connectedto a wiring 5655. A first terminal of the transistor 5651 is connectedto the wiring 5644. A second terminal of the transistor 5651 isconnected to a first electrode of the liquid crystal element 5652 and afirst electrode of the capacitor 5653. A second electrode of the liquidcrystal element 5652 corresponds to a counter electrode 5657. A secondelectrode of the capacitor 5653 is connected to a wiring 5646.

The wiring 5644 functions as a signal line. The wiring 5645 functions asa scan line. The wiring 5655 functions as a signal line. The wiring 5646functions as a capacitor line. Each of the transistor 5641 and thetransistor 5651 functions as a switch. Each of the capacitor 5643 andthe capacitor 5653 functions as a storage capacitor.

It is acceptable as long as each of the transistor 5641 and thetransistor 5651 functions as a switch, and each of the transistor 5641and the transistor 5651 may be either a P-channel transistor or anN-channel transistor.

A video signal input to the subpixel 5640 may be a value which isdifferent from that of a video signal input to the subpixel 5650. Inthis case, the viewing angle can be widened because alignment of liquidcrystal molecules of the liquid crystal element 5642 and alignment ofliquid crystal molecules of the liquid crystal element 5652 can bevaried from each other.

Note that although this embodiment mode is described with reference tovarious drawings, the contents (or may be part of the contents)described in each drawing can be freely applied to, combined with, orreplaced with the contents (or may be part of the contents) described inanother drawing. Further, even more drawings can be formed by combiningeach part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described ineach drawing of this embodiment mode can be freely applied to, combinedwith, or replaced with the contents (or may be part of the contents)described in a drawing in another embodiment mode. Further, even moredrawings can be formed by combining each part with part of anotherembodiment mode in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of thecontents (or may be part of the contents) described in other embodimentmodes, an example of slight transformation thereof, an example ofpartial modification thereof, an example of improvement thereof, anexample of detailed description thereof, an application example thereof,an example of related part thereof, or the like. Therefore, the contentsdescribed in other embodiment modes can be freely applied to, combinedwith, or replaced with this embodiment mode.

Embodiment Mode 5

In this embodiment mode, a pixel structure of a display device isdescribed. In particular, a pixel structure of a display device using anorganic EL element is described.

FIG. 25A shows an example of a top view (a layout diagram) of a pixelincluding two transistors. FIG. 25B shows an example of across-sectional view along X-X′ in FIG. 25A.

FIG. 25A shows a first transistor 6005, a first wiring 6006, a secondwiring 6007, a second transistor 6008, a third wiring 6011, a counterelectrode 6012, a capacitor 6013, a pixel electrode 6015, a partitionwall 6016, an organic conductive film 6017, an organic thin film 6018,and a substrate 6019. Note that it is preferable that the firsttransistor 6005 be used as a switching transistor, the first wiring 6006as a gate signal line, the second wiring 6007 as a source signal line,the second transistor 6008 as a driving transistor, and the third wiring6011 as a current supply line.

A gate electrode of the first transistor 6005 is electrically connectedto the first wiring 6006. One of a source electrode and a drainelectrode of the first transistor 6005 is electrically connected to thesecond wiring 6007. The other of the source electrode and the drainelectrode of the first transistor 6005 is electrically connected to agate electrode of the second transistor 6008 and one electrode of thecapacitor 6013. Note that the gate electrode of the first transistor6005 includes a plurality of gate electrodes. Accordingly, leakagecurrent in the off state of the first transistor 6005 can be reduced.

One of a source electrode and a drain electrode of the second transistor6008 is electrically connected to the third wiring 6011, and the otherof the source electrode and the drain electrode of the second transistor6008 is electrically connected to the pixel electrode 6015. Accordingly,current flowing to the pixel electrode 6015 can be controlled by thesecond transistor 6008.

The organic conductive film 6017 is provided over the pixel electrode6015, and the organic thin film 6018 (an organic compound layer) isprovided thereover. The counter electrode 6012 is provided over theorganic thin film 6018 (the organic compound layer). Note that thecounter electrode 6012 may be formed over the entire surface to beconnected to all the pixels in common, or may be patterned using ashadow mask or the like.

Light emitted from the organic thin film 6018 (the organic compoundlayer) is transmitted through either the pixel electrode 6015 or thecounter electrode 6012.

In FIG. 25B, the case where light is emitted to the pixel electrodeside, that is, a side on which the transistor and the like are formed isreferred to as bottom emission; and the case where light is emitted tothe counter electrode side is referred to as top emission.

In the case of bottom emission, it is preferable that the pixelelectrode 6015 be formed of a light-transmitting conductive film. On theother hand, in the case of top emission, it is preferable that thecounter electrode 6012 be formed of a light-transmitting conductivefilm.

In a light-emitting device for color display, EL elements havingrespective light emission colors of RGB may be separately formed, or anEL element with a single color may be applied over an entire surface andlight emission of RGB can be obtained by using a color filter.

Note that the structures shown in FIGS. 25A and 25B are examples, andvarious structures can be employed for a pixel layout, a cross-sectionalstructure, a stacking order of electrodes of an EL element, and thelike, other than the structures shown in FIGS. 25A and 25B. Further, asa light-emitting layer, various elements such as a crystalline elementsuch as an LED, and an element formed of an inorganic thin film can beused as well as the element formed of the organic thin film shown in thedrawing.

Note that although this embodiment mode is described with reference tovarious drawings, the contents (or may be part of the contents)described in each drawing can be freely applied to, combined with, orreplaced with the contents (or may be part of the contents) described inanother drawing. Further, even more drawings can be formed by combiningeach part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described ineach drawing of this embodiment mode can be freely applied to, combinedwith, or replaced with the contents (or may be part of the contents)described in a drawing in another embodiment mode. Further, even moredrawings can be formed by combining each part with part of anotherembodiment mode in the drawings of this embodiment mode.

This embodiment mode shows an example of an embodied case of thecontents (or may be part of the contents) described in other embodimentmodes, an example of slight transformation thereof, an example ofpartial modification thereof, an example of improvement thereof, anexample of detailed description thereof, an application example thereof,an example of related part thereof, or the like. Therefore, the contentsdescribed in other embodiment modes can be freely applied to, combinedwith, or replaced with this embodiment mode.

Embodiment Mode 6

In this embodiment mode, examples of electronic devices are described.

FIG. 26 shows a display panel module in which a display panel 9601 and acircuit board 9605 are combined. The display panel 9601 includes a pixelportion 9602, a scan line driver circuit 9603, and a signal line drivercircuit 9604. The circuit board 9605 is provided with a control circuit9606, a signal dividing circuit 9607, and the like, for example. Thedisplay panel 9601 and the circuit board 9605 are connected by aconnection wiring 9608. As the connection wiring, an FPC or the like canbe used.

FIG. 27 is a block diagram showing a main structure of a televisionreceiver. A tuner 9611 receives a video signal and an audio signal. Thevideo signal is processed by a video signal amplifier circuit 9612, avideo signal processing circuit 9613 for converting a signal output fromthe video signal amplifier circuit 9612 into a color signalcorresponding to each color of red, green, and blue, and a controlcircuit 9622 for converting the video signal into a signal which meetsinput specifications of a driver circuit. The control circuit 9622outputs signals to a scan line driver circuit 9624 and a signal linedriver circuit 9614. The scan line driver circuit 9624 and the signalline driver circuit 9614 drive a display panel 9621. In the case ofdigital driving, a structure may be used in which a signal dividingcircuit 9623 is provided on the signal line side and an input digitalsignal is divided into m (m is a positive integer) pieces to besupplied.

Among the signals received by the tuner 9611, the audio signal istransmitted to an audio signal amplifier circuit 9615, and outputthereof is supplied to a speaker 9617 through an audio signal processingcircuit 9616. A control circuit 9618 receives control information on areceiving station (reception frequency) and sound volume from an inputportion 9619, and transmits a signal to the tuner 9611 or the audiosignal processing circuit 9616.

FIG. 28A shows a television receiver incorporated with a display panelmodule which is different from that of FIG. 27. In FIG. 28A, a displayscreen 9632 stored in a housing 9631 is formed using the display panelmodule. Note that speakers 9633, input means (an operation key 9634, aconnection terminal 9635, a sensor 9636 (having a function to measurepower, displacement, position, speed, acceleration, angular velocity,the number of rotations, distance, light, liquid, magnetism,temperature, a chemical substance, sound, time, hardness, an electricfield, current, voltage, electric power, radiation, a flow rate,humidity, gradient, oscillation, smell, or infrared ray), and amicrophone 9637), and the like may be provided as appropriate.

FIG. 28B shows a television receiver, only a display of which can becarried wirelessly. The television receiver is provided with a displayportion 9643, a speaker portion 9647, input means (an operation key9646, a connection terminal 9648, a sensor 9649 (having a function tomeasure power, displacement, position, speed, acceleration, angularvelocity, the number of rotations, distance, light, liquid, magnetism,temperature, a chemical substance, sound, time, hardness, an electricfield, current, voltage, electric power, radiation, a flow rate,humidity, gradient, oscillation, smell, or infrared ray), and amicrophone 9641), and the like as appropriate. A battery and a signalreceiver are incorporated in a housing 9642. The battery drives thedisplay portion 9643, the speaker portion 9647, the sensor 9649, and themicrophone 9641. The battery can be repeatedly charged by a charger9640. The charger 9640 can transmit and receive a video signal andtransmit the video signal to the signal receiver of the display. Thedevice in FIG. 28B is controlled by the operation key 9646.Alternatively, the device in FIG. 28B can transmit a signal to thecharger 9640 by operating the operation key 9646. That is, the devicemay be a video-audio two-way communication device. Furtheralternatively, by operating the operation key 9646, the device in FIG.28B may transmit a signal to the charger 9640, and another electronicdevice is made to receive a signal which can be transmitted from thecharger 9640; thus, the device in FIG. 28B can control communication ofanother electronic device. That is, the device may be a general-purposeremote control device. Note that the contents (or part thereof)described in each drawing of this embodiment mode can be applied to thedisplay portion 9643.

Next, a structural example of a mobile phone is described with referenceto FIG. 29.

A display panel 9662 is detachably incorporated in a housing 9650. Theshape and size of the housing 9650 can be changed as appropriate inaccordance with the size of the display panel 9662. The housing 9650which fixes the display panel 9662 is fitted in a printed wiring board9651 to be assembled as a module.

The display panel 9662 is connected to the printed wiring board 9651through an FPC 9663. The printed wiring board 9651 is provided with aspeaker 9652, a microphone 9653, a transmitting/receiving circuit 9654,a signal processing circuit 9655 including a CPU, a controller, and thelike, and a sensor 9661 (having a function to measure power,displacement, position, speed, acceleration, angular velocity, thenumber of rotations, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, electric power, radiation, a flow rate, humidity, gradient,oscillation, smell, or infrared ray). Such a module, an operation key9656, a battery 9657, and an antenna 9660 are combined and stored in ahousing 9659. A pixel portion of the display panel 9662 is provided tobe viewed from an opening window formed in the housing 9659.

In the display panel 9662, the pixel portion and part of peripheraldriver circuits (a driver circuit having a low operation frequency amonga plurality of driver circuits) may be formed over the same substrate byusing transistors, and another part of the peripheral driver circuits (adriver circuit having a high operation frequency among the plurality ofdriver circuits) may be formed over an IC chip. Then, the IC chip may bemounted on the display panel 9662 by COG (Chip On Glass). Alternatively,the IC chip may be connected to a glass substrate by using TAB (TapeAutomated Bonding) or a printed wiring board. By employing such astructure, the power consumption of a display device can be reduced, anda portable phone device can be used for a longer period per charge. Costreduction of the mobile phone can be achieved.

The mobile phone shown in FIG. 29 has various functions such as afunction of displaying a variety of information (e.g., a still image, amoving image, and a text image); a function of displaying a calendar, adate, time, or the like on a display portion; a function of operating orediting the information displayed on the display portion; a function ofcontrolling processing by a variety of software (programs); a wirelesscommunication function; a function of communicating with another mobilephone, a fixed phone, or an audio communication device by using thewireless communication function; a function of connecting with a varietyof computer networks by using the wireless communication function; afunction of transmitting or receiving a variety of data by using thewireless communication function; a function of operating a vibrator inaccordance with incoming call, reception of data, or an alarm; and afunction of generating a sound in accordance with incoming call,reception of data, or an alarm. Note that functions of the mobile phoneshown in FIG. 29 are not limited to them, and the mobile phone can havevarious functions.

FIG. 30A shows a display, which includes a housing 9671, a support base9672, a display portion 9673, a speaker 9677, an LED lamp 9679, inputmeans (a connection terminal 9674, a sensor 9675 (having a function tomeasure power, displacement, position, speed, acceleration, angularvelocity, the number of rotations, distance, light, liquid, magnetism,temperature, a chemical substance, sound, time, hardness, an electricfield, current, voltage, electric power, radiation, a flow rate,humidity, gradient, oscillation, smell, or infrared ray), a microphone9676, and an operation key 9678), and the like. The display shown inFIG. 30A has a function of displaying a variety of information (e.g., astill image, a moving image, and a text image) on the display portion.The display shown in FIG. 30A are not limited to these functions, andthe display can have various functions.

FIG. 30B shows a camera, which includes a main body 9691, a displayportion 9692, a shutter button 9696, a speaker 9700, an LED lamp 9701,input means (an image receiving portion 9693, operation keys 9694, anexternal connection port 9695, a connection terminal 9697, a sensor 9698(having a function to measure power, displacement, position, speed,acceleration, angular velocity, the number of rotations, distance,light, liquid, magnetism, temperature, a chemical substance, sound,time, hardness, an electric field, current, voltage, electric power,radiation, a flow rate, humidity, gradient, oscillation, smell, orinfrared ray), and a microphone 9699), and the like. The camera shown inFIG. 30B has a function of photographing a still image and a movingimage; a function of automatically correcting the photographed image(the still image or the moving image); a function of storing thephotographed image in a recording medium (provided outside orincorporated in the camera); and a function of displaying thephotographed image on the display portion. Note that the functions ofthe camera shown in FIG. 30B are not limited to these functions, and thecamera can have various functions.

FIG. 30C illustrates a computer, which includes a main body 9711, ahousing 9712, a display portion 9713, a speaker 9720, an LED lamp 9721,a reader/writer 9722, input means (a keyboard 9714, an externalconnection port 9715, a pointing device 9716, a connection terminal9717, a sensor 9718 (having a function to measure power, displacement,position, speed, acceleration, angular velocity, the number ofrotations, distance, light, liquid, magnetism, temperature, a chemicalsubstance, sound, time, hardness, an electric field, current, voltage,electric power, radiation, a flow rate, humidity, gradient, oscillation,smell, or infrared ray), and a microphone 9719), and the like. Thecomputer shown in FIG. 30C has a function of displaying a variety ofinformation (e.g., a still image, a moving image, and a text image) onthe display portion; a function of controlling processing by a varietyof software (programs); a communication function such as wirelesscommunication or wire communication; a function of connecting to variouscomputer networks by using the communication function; and a function oftransmitting or receiving a variety of data by using the communicationfunction. Note that the functions of the computer shown in FIG. 30C arenot limited to these functions, and the computer can have variousfunctions.

FIG. 37A illustrates a mobile computer, which includes a main body 9791,a display portion 9792, a switch 9793, a speaker 9799, an LED lamp 9800,input means (operation keys 9794, an infrared port 9795, a connectionterminal 9796, a sensor 9797 (having a function to measure power,displacement, position, speed, acceleration, angular velocity, thenumber of rotations, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, electric power, radiation, a flow rate, humidity, gradient,oscillation, smell, or infrared ray), and a microphone 9798), and thelike. The mobile computer shown in FIG. 37A has a function of displayinga variety of information (e.g., a still image, a moving image, and atext image) on the display portion; a touch panel function on thedisplay portion; a function of displaying a calendar, a date, time, andthe like on the display portion; a function of controlling processing bya variety of software (programs); a wireless communication function; afunction of connecting to various computer networks by using thewireless communication function; and a function of transmitting orreceiving a variety of data by using the wireless communicationfunction. Note that the functions of the mobile computer shown in FIG.37A are not limited to these functions, and the mobile computer can havevarious functions.

FIG. 37B illustrates a portable image reproducing device having arecording medium (e.g., a DVD player), which includes a main body 9811,a housing 9812, a display portion A 9813, a display portion B 9814, aspeaker portion 9817, an LED lamp 9821, input means (a recording medium(e.g., DVD) reading portion 9815, operation keys 9816, a connectionterminal 9818, a sensor 9819 (having a function to measure power,displacement, position, speed, acceleration, angular velocity, thenumber of rotations, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, electric power, radiation, a flow rate, humidity, gradient,oscillation, smell, or infrared ray), and a microphone 9820), and thelike. The display portion A 9813 mainly displays image information andthe display portion B 9814 mainly displays text information.

FIG. 37C illustrates a goggle-type display, which includes a main body9031, a display portion 9032, an earphone 9033, a support portion 9034,an LED lamp 9039, a speaker 9038, input means (a connection terminal9035, a sensor 9036 (having a function to measure power, displacement,position, speed, acceleration, angular velocity, the number ofrotations, distance, light, liquid, magnetism, temperature, a chemicalsubstance, sound, time, hardness, an electric field, current, voltage,electric power, radiation, a flow rate, humidity, gradient, oscillation,smell, or infrared ray), and a microphone 9037), and the like. Thegoggle-type display shown in FIG. 37C has a function of displaying animage (e.g., a still image, a moving image, or a text image) which isexternally obtained on the display portion. Note that the functions ofthe goggle-type display shown in FIG. 37C are not limited to thesefunctions, and the goggle-type display can have various functions.

FIG. 38A illustrates a portable game machine, which includes a housing9851, a display portion 9852, a speaker portion 9853, a recording mediuminsert portion 9855, an LED lamp 9859, input means (an operation key9854, a connection terminal 9856, a sensor 9857 (having a function tomeasure power, displacement, position, speed, acceleration, angularvelocity, the number of rotations, distance, light, liquid, magnetism,temperature, a chemical substance, sound, time, hardness, an electricfield, current, voltage, electric power, radiation, a flow rate,humidity, gradient, oscillation, smell, or infrared ray), and amicrophone 9858), and the like. The portable game machine shown in FIG.38A has functions for reading out programs and data stored in storagemedia and displaying the information on a display. The portable gamemachine shown in FIG. 38A has a function of sharing information withanother portable game machine by wireless communication. Note that thefunctions of the portable game machine shown in FIG. 38A are not limitedto these functions, and the portable game machine can have variousfunctions.

FIG. 38A shows a digital camera having a television reception function,which includes a housing 9861, a display portion 9862, a speaker 9864, ashutter button 9865, an LED lamp 9871, input means (an operation key9863, an image receiving portion 9866, an antenna 9867, a connectionterminal 9868, a sensor 9869 (having a function to measure power,displacement, position, speed, acceleration, angular velocity, thenumber of rotations, distance, light, liquid, magnetism, temperature, achemical substance, sound, time, hardness, an electric field, current,voltage, electric power, radiation, a flow rate, humidity, gradient,oscillation, smell, or infrared ray), and a microphone 9870), and thelike. The digital camera having the television reception function, whichis shown in FIG. 38B, has a function of photographing a still image anda moving image; a function of automatically correcting the photographedimage; a function of obtaining a variety of information from theantenna; a function of storing the photographed image or the informationobtained from the antenna; and a function of displaying the photographedimage or the information obtained from the antenna on the displayportion. Note that the functions of the digital camera having thetelevision reception function, which is shown in FIG. 38B, are notlimited to these functions, and the digital camera having the televisionreception function can have various functions.

FIG. 39 illustrates a portable game machine, which includes a housing9881, a first display portion 9882, a second display portion 9883, aspeaker portion 9884, a recording medium insert portion 9886, an LEDlamp 9890, input means (an operation key 9885, a connection terminal9887, a sensor 9888 (having a function to measure power, displacement,position, speed, acceleration, angular velocity, the number ofrotations, distance, light, liquid, magnetism, temperature, a chemicalsubstance, sound, time, hardness, an electric field, current, voltage,electric power, radiation, a flow rate, humidity, gradient, oscillation,smell, or infrared ray), and a microphone 9889), and the like. Theportable game machine shown in FIG. 39 has a function of reading aprogram or data stored in the recording medium to display it on thedisplay portion, and a function of sharing information with anotherportable game machine by wireless communication. Note that the functionsof the portable game machine shown in FIG. 39 are not limited to thesefunctions, and the portable game machine can have various functions.

As shown in FIGS. 30A to 30C, 37A to 37C, 38A to 38C, and 39, theelectronic device includes a display portion for displaying some kind ofinformation. The electronic device is low power consumption, and candrive with a battery for a long time. Alternatively, a manufacturingmethod is simple, and manufacturing cost can be reduced.

Next, application examples of a semiconductor device are described.

FIG. 31 shows an example in which the semiconductor device isincorporated in a structure. FIG. 31 shows a housing 9730, a displaypanel 9731, a remote controller 9732 which is an operation portion, aspeaker portion 9733, and the like. The semiconductor device isincorporated in the structure as a wall-hanging type, so that thesemiconductor device can be provided without requiring a wide space.

FIG. 32 shows another example in which the semiconductor device isincorporated in a structure. A display panel 9741 is incorporated in aprefabricated bath unit 9742, so that a bather can view the displaypanel 9741. The display panel 9741 has a function of displayinginformation by an operation of the bather. The display panel 9741 can beutilized for advertisement or an amusement means.

Note that the semiconductor device can be provided in various places aswell as on a sidewall of the prefabricated bath unit 9742 shown in FIG.32. For example, the semiconductor device may be incorporated in part ofa mirror or the bathtub itself. At this time, the shape of the displaypanel 9741 may be a shape in accordance with the mirror or the bathtub.

FIG. 33 shows another example in which the semiconductor device isincorporated in a structure. Display panels 9752 are curved inaccordance with curved surfaces of columnar objects 9751. Note thathere, the columnar objects 9751 are described as telephone poles.

The display panels 9752 shown in FIG. 33 are provided in positionshigher than a human eye level. When the display panels 9752 are providedfor structures standing outside to each other in large numbers, such astelephone poles, advertising can be performed to an unspecified numberof viewers. Here, since the display panels 9752 can easily display thesame images by control from outside and can easily switch imagesinstantly, extremely effective information display and advertisingeffects can be expected. When self-luminous display elements areprovided in the display panels 9752, the display panels 9752 areeffectively used as highly visible display media even at night. When thedisplay panels 9752 are provided for the telephone poles, power supplymeans of the display panels 9752 can be easily secured. In an emergencysuch as a disaster, the display panels 9752 can be means for quicklytransmitting precise information to victims.

Note that as each of the display panels 9752, a display panel in which adisplay element is driven by providing a switching element such as anorganic transistor over a film-like substrate so that an image isdisplayed can be used.

Note that although this embodiment describes the wall, the prefabricatedbath unit, and the columnar object as examples of the structure, thisembodiment mode is not limited to this, and the semiconductor device canbe provided for various structures.

Next, an example is described in which the semiconductor device isincorporated in a moving object.

FIG. 34 shows an example in which the semiconductor device isincorporated in a car. A display panel 9762 is incorporated in a carbody 9761 of the car and can display information on an operation of thecar or information input from inside or outside of the car on anon-demand basis. Note that the display panel 9762 may have a navigationfunction.

Note that the semiconductor device can be provided in various positionsas well as the car body 9761 shown in FIG. 34. For example, thesemiconductor device may be incorporated in a glass window, a door, ashift lever, a seat, a room mirror, or the like. At this time, the shapeof the display panel 9762 may be a shape in accordance with a shape ofan object in which the display panel 9762 is provided.

FIGS. 35A and 35B each show an example in which the semiconductor deviceis incorporated in a train car.

FIG. 35A shows an example in which display panels 9772 are provided forglasses of a door 9771 of the train car. The display panels 9772 have anadvantage over conventional paper-based advertisement that labor costwhich is necessary for switching advertisement is not needed. Since thedisplay panels 9772 can instantly switch images displayed on displayportions by external signals, images on the display panels can beswitched as the type of train passenger changes in accordance withdifferent time periods, for example, so that a more effectiveadvertising effect can be expected.

FIG. 35B shows an example in which display panels 9772 are provided forglass windows 9773 and a ceiling 9774 as well as the glasses of thedoors 9771 of the train car. Since the semiconductor device can beeasily provided in a position in which the semiconductor device isconventionally difficult to be provided in this manner, an effectiveadvertisement effect can be obtained. Since the semiconductor device caninstantly switch images displayed on the display portion by externalsignals, cost and time generated in advertisement switching can bereduced, so that more flexible advertisement operation and informationtransmission can be performed.

Note that the semiconductor device can be provided in various positionsas well as the doors 9771, the glass windows 9773, and the ceiling 9774which are shown in FIGS. 35A and 35B. For example, the semiconductordevice may be incorporated in a hand strap, a seat, a handrail, a floor,or the like. At this time, the shape of the display panel 9772 may be ashape in accordance with a shape of an object in which the display panel9772 is provided.

FIGS. 36A and 36B each show an example in which the semiconductor deviceis incorporated in a passenger airplane.

FIG. 36A shows a shape in use when a display panel 9782 is provided fora ceiling 9781 above a seat of the passenger airplane. The display panel9782 is incorporated in the ceiling 9781 through a hinge portion 9783,and a passenger can view the display panel 9782 by a telescopic motionof the hinge portion 9783. The display panel 9782 has a function ofdisplaying information by an operation of the passenger. The displaypanel 9782 can be utilized for advertisement or an amusement means. Whenthe display panel 9782 is stored on the ceiling 9781 by folding thehinge portion 9783 as shown in FIG. 36B, safety during takeoff andlanding can be secured. Note that the display panel 9782 can also beutilized as a medium and a guide light by lighting display elements ofthe display panel 9782 in an emergency.

Note that the semiconductor device can be incorporated in variouspositions as well as the ceiling 9781 shown in FIGS. 36A and 36B. Forexample, the semiconductor device may be incorporated in a seat, atable, an armrest, a window, or the like. A large display panel whichcan be viewed simultaneously by a plurality of persons may be providedon a wall of an airframe. At this time, the shape of the display panel9782 may be a shape in accordance with a shape of an object in which thedisplay panel 9782 is provided.

Note that although this embodiment mode describes the train car body,the car body, and the airplane body as examples of moving objects, thepresent invention is not limited to them, and the semiconductor devicecan be provided in various objects such as a motorbike, a four-wheeledvehicle (including a car, a bus, and the like), a train (including amonorail, a railroad, and the like), and a vessel. Since display ondisplay panels in a moving object can be switched instantly by externalsignals, the semiconductor device can be used for an advertisementdisplay board for an unspecified number of customers, an informationdisplay board in an emergency, or the like by providing thesemiconductor device in the moving object.

Note that although this embodiment mode is described with reference tovarious drawings, the contents (or may be part of the contents)described in each drawing can be freely applied to, combined with, orreplaced with the contents (or may be part of the contents) described inanother drawing. Further, even more drawings can be formed by combiningeach part with another part in the above-described drawings.

Similarly, the contents (or may be part of the contents) described ineach drawing of this embodiment mode can be freely applied to, combinedwith, or replaced with the contents (or may be part of the contents)described in a drawing in another embodiment mode. Further, even moredrawings can be formed by combining each part with part of anotherembodiment mode in the drawings of this embodiment mode.

Note that this embodiment mode shows an example of an embodied case ofthe contents (or may be part of the contents) described in otherembodiment modes, an example of slight transformation thereof, anexample of partial modification thereof, an example of improvementthereof, an example of detailed description thereof, an applicationexample thereof, an example of related part thereof, or the like.Therefore, the contents described in other embodiment modes can befreely applied to, combined with, or replaced with this embodiment mode.

This application is based on Japanese Patent Application serial No.2007-173311 filed with Japan Patent Office on Jun. 29, 2007, the entirecontents of which are hereby incorporated by reference.

1. A semiconductor device comprising: a first semiconductor layer over asubstrate; a first insulating layer over the first semiconductor layer;a first conductive layer and a second conductive layer over the firstinsulating layer; a second insulating layer over the first conductivelayer and the second conductive layer; a second semiconductor layer overthe second insulating layer; and a third conductive layer over thesecond semiconductor layer, wherein the first semiconductor layercomprises a single-crystal silicon, wherein the first conductive layeris overlapped with the first semiconductor layer, and the secondconductive layer is overlapped with the second semiconductor layer;wherein the first semiconductor layer serves as an active layer of afirst transistor; wherein the second semiconductor layer serves as anactive layer of a second transistor; wherein a property of the firstsemiconductor layer is different from a property of the secondsemiconductor layer, and wherein the second semiconductor layercomprises a non-single-crystal semiconductor having crystallinity. 2.The semiconductor device according to claim 1, wherein the firstinsulating layer serves as a gate insulating layer of the firsttransistor, and wherein the first conductive layer serves as a gateelectrode of the first transistor.
 3. The semiconductor device accordingto claim 1, wherein the second insulating layer serves as a gateinsulating layer of the second transistor, and wherein the secondconductive layer serves as a gate electrode of the second transistor. 4.The semiconductor device according to claim 1, wherein the thirdconductive layer is electrically connected to the second semiconductorlayer.
 5. The semiconductor device according to claim 1, wherein thesecond semiconductor layer includes a microcrystalline semiconductor. 6.A display device, comprising the semiconductor device according to claim1 and a display element.
 7. A liquid crystal display device comprisingthe semiconductor device according to claim 1 and a display element. 8.An electronic device, comprising the display device according to claim 6and an operation switch.
 9. An electronic device, comprising the liquidcrystal display device according to claim 7 and an operation switch. 10.A semiconductor device comprising: a first semiconductor layer over aninsulating substrate; a first insulating layer over the firstsemiconductor layer; a first conductive layer and a second conductivelayer over the first insulating layer; a second insulating layer overthe first conductive layer and the second conductive layer; a secondsemiconductor layer over the second insulating layer; and a thirdconductive layer over the second semiconductor layer, wherein the firstsemiconductor layer comprises a single-crystal silicon, wherein thefirst conductive layer is overlapped with the first semiconductor layer,and the second conductive layer is overlapped with the secondsemiconductor layer; wherein the first semiconductor layer serves as anactive layer of a first transistor; wherein the second semiconductorlayer serves as an active layer of a second transistor; wherein aproperty of the first semiconductor layer is different from a propertyof the second semiconductor layer and wherein the second semiconductorlayer comprises a non-single-crystal semiconductor having crystallinity.11. The semiconductor device according to claim 10, wherein the firstinsulating layer serves as a gate insulating layer of the firsttransistor, and wherein the first conductive layer serves as a gateelectrode of the first transistor.
 12. The semiconductor deviceaccording to claim 10, wherein the second insulating layer serves as agate insulating layer of the second transistor, and wherein the secondconductive layer serves as a gate electrode of the second transistor.13. The semiconductor device according to claim 10, wherein the thirdconductive layer is electrically connected to the second semiconductorlayer.
 14. The semiconductor device according to claim 10, wherein thesecond semiconductor layer includes a microcrystalline semiconductor.15. A display device, comprising the semiconductor device according toclaim 10 and a display element.
 16. A liquid crystal display devicecomprising the semiconductor device according to claim 10 and a displayelement.
 17. An electronic device, comprising the display deviceaccording to claim 15 and an operation switch.
 18. An electronic device,comprising the liquid crystal display device according to claim 16 andan operation switch.
 19. A semiconductor device comprising: a firstsemiconductor layer over an insulating substrate, the firstsemiconductor layer having crystallinity; a first insulating layer overthe first semiconductor layer; a first conductive layer and a secondconductive layer over the first insulating layer; a second insulatinglayer over the first conductive layer and the second conductive layer; asecond semiconductor layer over the second insulating layer; a thirdconductive layer over the second semiconductor layer; a fourthconductive layer over the second insulating layer; a third insulatinglayer over the third conductive layer and the fourth conductive layer;and a fifth conductive layer over the third insulating layer, whereinthe first semiconductor layer comprises a single-crystal silicon,wherein the first conductive layer is overlapped with the firstsemiconductor layer, and the second conductive layer is overlapped withthe second semiconductor layer; wherein the first semiconductor layerserves as an active layer of a first transistor; wherein the secondsemiconductor layer serves as an active layer of a second transistor;wherein a property of the first semiconductor layer is different from aproperty of the second semiconductor layer and wherein the secondsemiconductor layer comprises a non-single-crystal semiconductor havingcrystallinity.
 20. The semiconductor device according to claim 19,wherein the first insulating layer serves as a gate insulating layer ofthe first transistor, and wherein the first conductive layer serves as agate electrode of the first transistor.
 21. The semiconductor deviceaccording to claim 19, wherein the second insulating layer serves as agate insulating layer of the second transistor, and wherein the secondconductive layer serves as a gate electrode of the second transistor.22. The semiconductor device according to claim 19, wherein the fifthconductive layer is electrically connected to the fourth conductivelayer through a contact hole provided in the third insulating layer. 23.The semiconductor device according to claim 19, wherein the fifthconductive layer is electrically connected to the first semiconductorlayer through a contact hole provided in the first insulating layer, thesecond insulating layer and the third insulating layer.
 24. Thesemiconductor device according to claim 19, wherein the third conductivelayer is electrically connected to the second semiconductor layer. 25.The semiconductor device according to claim 19, wherein the secondsemiconductor layer includes a microcrystalline semiconductor.
 26. Adisplay device, comprising the semiconductor device according to claim19 and a display element.
 27. A liquid crystal display device comprisingthe semiconductor device according to claim 19 and a display element.28. An electronic device, comprising the display device according toclaim 26 and an operation switch.
 29. An electronic device, comprisingthe liquid crystal display device according to claim 27 and an operationswitch.